Anatomy: Penis

FIG. 1154– The constituent cavernous cylinders of the penis. The glans and anterior part of the corpus cavernosum urethræ are detached from the corpora cavernosa penis and turned to one side.

The penis is a pendulous organ suspended from the front and sides of the pubic arch and containing the greater part of the urethra. In the flaccid condition it is cylindrical in shape, but when erect assumes the form of a triangular prism with rounded angles, one side of the prism forming the dorsum. It is composed of three cylindrical masses of cavernous tissue bound together by fibrous tissue and covered with skin. Two of the masses are lateral, and are known as the corpora cavernosa penis; the third is median, and is termed thecorpus cavernosum urethræ (Figs. 1154, 1155).

The Corpora Cavernosa Penis form the greater part of the substance of the penis. For their anterior three-fourths they lie in intimate apposition with one another, but behind they diverge in the form of two tapering processes, known as the crura, which are firmly connected to the rami of the pubic arch. Traced from behind forward, each crus begins by a blunt-pointed process in front of the tuberosity of the ischium. Just before it meets its fellow it presents a slight enlargement, named by Kobelt the bulb of the corpus cavernosum penis. Beyond this point the crus undergoes a constriction and merges into the corpus cavernosum proper, which retains a uniform diameter to its anterior end. Each corpus cavernosum penis ends abruptly in a rounded extremity some distance from the point of the penis.

The corpora cavernosa penis are surrounded by a strong fibrous envelope consisting of superficial and deep fibers. The superficial fibers are longitudinal in direction, and form a single tube which encloses both corpora; the deep fibers are arranged circularly around each corpus, and form by their junction in the median plane the septum of the penis. This is thick and complete behind, but is imperfect in front, where it consists of a series of vertical bands arranged like the teeth of a comb; it is therefore named the septum pectiniforme.

The Corpus Cavernosum Urethræ (corpus spongiosum) contains the urethra. Behind, it is expanded to form the urethral bulb, and lies in apposition with the inferior fascia of the urogenital diaphragm, from which it receives a fibrous investment. The urethra enters the bulb nearer to the upper than to the lower surface. On the latter there is a median sulcus, from which a thin fibrous septum projects into the substance of the bulb and divides it imperfectly into two lateral lobes or hemispheres.

FIG. 1155– Transverse section of the penis.

The portion of the corpus cavernosum urethræ in front of the bulb lies in a groove on the under surface of the conjoined corpora cavernosa penis. It is cylindrical in form and tapers slightly from behind forward. Its anterior end is expanded in the form of an obtuse cone, flattened from above downward. This expansion, termed the glans penis, is moulded on the rounded ends of the corpora cavernosa penis, extending farther on their upper than on their lower surfaces. At the summit of the glans is the slit-like vertical external urethral orifice. The circumference of the base of the glans forms a rounded projecting border, thecorona glandis, overhanging a deep retroglandular sulcus, behind which is the neckof the penis.

For descriptive purposes it is convenient to divide the penis into three regions: the root,the body, and the extremity.

FIG. 1156– Vertical section of bladder, penis, and urethra.

The root (radix penis) of the penis is triradiate in form, consisting of the diverging crura, one on either side, and the median urethral bulb. Each crus is covered by the Ischiocavernosus, while the bulb is surrounded by the Bulbocavernosus. The root of the penis lies in the perineum between the inferior fascia of the urogenital diaphragm and the fascia of Colles. In addition to being attached to the fasciæ and the pubic rami, it is bound to the front of the symphysis pubis by the fundiform and suspensory ligaments. Thefundiform ligament springs from the front of the sheath of the Rectus abdominis and the linea alba; it splits into two fasciculi which encircle the root of the penis. The upper fibers of the suspensory ligament pass downward from the lower end of the linea alba, and the lower fibers from the symphysis pubis; together they form a strong fibrous band, which extends to the upper surface of the root, where it blends with the fascial sheath of the organ.

The body (corpus penis) extends from the root to the ends of the corpora cavernosa penis, and in it these corpora cavernosa are intimately bound to one another. A shallow groove which marks their junction on the upper surface lodges the deep dorsal vein of the penis, while a deeper and wider groove between them on the under surface contains the corpus cavernosum urethræ. The body is ensheathed by fascia, which is continuous above with the fascia of Scarpa, and below with the dartos tunic of the scrotum and the fascia of Colles.

The extremity is formed by the glans penis, the expanded anterior end of the corpus cavernosum urethræ. It is separated from the body by the constricted neck, which is overhung by the corona glandis.

The integument covering the penis is remarkable for its thinness, its dark color, its looseness of connection with the deeper parts of the organ, and its absence of adipose tissue. At the root of the penis it is continuous with that over the pubes, scrotum, and perineum. At the neck it leaves the surface and becomes folded upon itself to form theprepuce or foreskin. The internal layer of the prepuce is directly continuous, along the line of the neck, with the integument over the glans. Immediately behind the external urethral orifice it forms a small secondary reduplication, attached along the bottom of a depressed median raphé, which extends from the meatus to the neck; this fold is termed thefrenulum of the prepuce. The integument covering the glans is continuous with the urethral mucous membrane at the orifice; it is devoid of haris, but projecting from its free surface are a number of small, highly sensitive papillæ. Scattered glands on the corona, neck, glans and inner layer of the prepuce, the preputial glands, have been described. (*178They secrete a sebaceous material of very peculiar odor, which probably contains casein, and readily undergoes decomposition; when mixed with discarded epithelial cells it is called smegma.

The prepuce covers a variable amount of the glans, and is separated from it by a potential sac—the preputial sac—which presents two shallow fossæ, one on either side of the frenulum.

Structure of the Penis.

—From the internal surface of the fibrous envelope of the corpora cavernosa penis, as well as from the sides of the septum, numerous bands or cords are given off, which cross the interior of these corpora cavernosa in all directions, subdividing them into a number of separate compartments, and giving the entire structure a spongy appearance (Fig. 1157). These bands and cords are called trabeculæ, and consist of white fibrous tissue, elastic fibers, and plain muscular fibers. In them are contained numerous arteries and nerves. The component fibers which form the trabeculæ are larger and stronger around the circumference than at the centers of the corpora cavernosa; they are also thicker behind than in front. The interspaces (cavernous spaces), on the contrary, are larger at the center than at the circumference, their long diameters being directed transversely. They are filled with blood, and are lined by a layer of flattened cells similar to the endothelial lining of veins.

The fibrous envelope of the corpus cavernosum urethræ is thinner, whiter in color, and more elastic than that of the corpora cavernosa penis. The trabeculæ are more delicate, nearly uniform in size, and the meshes between them smaller than in the corpora cavernosa penis: their long diameters, for the most part, corresponding with that of the penis. The external envelope or outer coat of the corpus cavernosum urethræ is formed partly of unstriped muscular fibers, and a layer of the same tissue immediately surrounds the canal of the urethra.

FIG. 1157– Section of corpus cavernosum penis in a non-distended condition. (Cadiat.) a.Trabeculæ of connective tissue, with many elastic fibers and bundles of plain muscular tissue, some of which are cut across (c). b. Blood sinuses.

Vessels and Nerves.—The arteries bringing the blood to the cavernous spaces are the deep arteries of the penis and branches from the dorsal arteries of the penis, which perforate the fibrous capsule, along the upper surface, especially near the forepart of the organ. On entering the cavernous structure the arteries divide into branches, which are supported and enclosed by the trabeculæ. Some of these arteries end in a capillary net-work, the branches of which open directly into the cavernous spaces; others assume a tendril-like appearance, and form convoluted and somewhat dilated vessels, which were named by Müller helicine arteries. They open into the spaces, and from them are also given off small capillary branches to supply the trabecular structure. They are bound down in the spaces by fine fibrous processes, and are most abundant in the back part of the corpora cavernosa (Fig. 1157).

FIG. 1158– Diagram of the arteries of the penis. (Testut.)

The blood from the cavernous spaces is returned by a series of vessels, some of which emerge in considerable numbers from the base of the glans penis and converge on the dorsum of the organ to form the deep dorsal vein; others pass out on the upper surface of the corpora cavernosa and join the same vein; some emerge from the under surface of the corpora cavernosa penis and receiving branches from the corpus cavernosum urethræ, wind around the sides of the penis to end in the deep dorsal vein; but the greater number pass out at the root of the penis and join the prostatic plexus.

The lymphatic vessels of the penis are described on page 713.

The nerves are derived from the pudendal nerve and the pelvic plexuses. On the glans and bulb some filaments of the cutaneous nerves have Pacinian bodies connected with them, and, according to Krause, many of them end in peculiar endbulbs (see page 1060).

FIG. 1159– Veins of the penis. (Testut.)

Note 178.  Stieda (Comptes-rendus du XII Congrés International de Médecine, Moscow, 1897) asserts that glands are never found on the corona glandis, and that what have hitherto been mistaken for glands are really large papillæ.

Diagnostic Pharmaceuticals

Plasma levels of Iodinated agents depend on:

1. Rate of administration (IV bolus, IV drip)
2. Blood half life
3. Distribution:
1. Rapid exchange between plasma and ECF
2. Exclusion form intracellular space
3. Do not cross the BBB intact
4. Excretion 
1. Glomerular filtration with no resorption in the tubules. 
2. Hepatic excretion (vicarious) increases in renal failure

Renographin

1.  

Anatomy: The Neck, Anatomy, Superficial Structures of the Neck

Sternocleidomastoid Muscle. 

It also acts as an accessory muscle of inspiration, along with the scalene muscles of the neck

Sternocleidomastoid
The triangles of the neck. (Anterior triangles to the left; posterior triangles to the right.)
Muscles of the neck. Lateral view.
Latin	musculus sternocleidomastoideus
Gray's	subject #111 390
Origin	manubrium sterni, medial portion of the clavicle
Insertion	mastoid process of the temporal bone, superior nuchal line of the occipital bone
Artery	occipital artery and the superior thyroid artery
Nerve	motor: accessory nerve sensory: cervical plexus (ventral ramus of the second cranial nerve)
Actions	Acting alone, tilts head to its own side and rotates it so the face is turned towards the opposite side. Acting together, flexes the neck, raises the sternum and assists in forced inspiration.

.

The Sternocleidomastoid is crossed by the platysma and the External Jugular Vein. The Sternocleidomastoid covers the great vessels of the neck and the cervical plexus of the nerves. 

Congenital torticollis: The Sternocleidomastoid may be injured at birth resulting in congenital torticollis. There is fixed rotation and tilting of the head owing to contracture of the sternocleidomastoid muscle. Birth injury, tearing fibers of the muscle during NVD vaginal delivery - bleeding - swelling and then fibrosis of the sternocleidomastoid. This shortening of the muscle is evident at age 3 to 4 when the neck elongates. Managed by physiotherapy that promotes daily stretching and tilting the head. 

Spasmodic torticollis may develop in adults - Stiff neck. 

 

Posterior Triangle of the Neck. 

The Sternocleidomastoid, the Trapezius and Clavicle form the posterior triangle of the neck. The trapezius and the Sternocleidomastoid meet at the superior nuchal line - where the Occipital Artery passes through the apex of the posterior triangle, before it ascends over the posterior aspect of the head.

The roof of the Posterior triangle of the Neck -  Covered by deep fascia and superficial to this fascia is the Platysma veins, nerves and skin.

The muscular FLOOR of the posterior triangle is formed by splenius capitus, levator scapulae, scalenus medius and scaleneus posterior muscles. The four mascles are covered by a carpet of Deep Cervical Fascia. The Spenius capitus muscle arises from the the ligamentum nuchae and the spinous process of the superior thoracic vertebrae. The Spenius Capitus runs superolaterally and inserts into the mastoid process.
Levator scapulae muscle lifts the scapula, arises from the first 4 cervical vertebrae and inserts into the medial boarder of the scapulae.
Scalenus Posterior Muscle arises from the lower two to three cervical vertebrae (4th, 5th, 6th cervical vertebrae) and inserts into the 2nd rib.
Scalenus Medius Muscle arises from the posterior tubercles of  ALL the cervical vertebrae. Inserts on the posterior part of the 1st rib. The Scalenus medius lies posterior to the roots of the brachial plexus.

Levator scapulae muscle
Muscles connecting the upper extremity to thevertebral column. (Levator scapula visible at upper right, at the neck.)
Latin	musculus levator scapulae
Gray's	subject #121 435
Origin	Posterior tubercles oftransverse processes of C1 - C4 vertebrae
Insertion	Superior part of medial border of scapula
Artery	dorsal scapular artery
Nerve	cervical nerve (C3, C4) anddorsal scapular nerve (C5)
Actions	Elevates scapula and tilts itsglenoid cavity inferiorly by rotating scapula

Contents of the Posterior Triangle:  Vessels and nerves of the Neck and Upper Limb'


The External Jugular Vein begins near the angle of the mandible, inferior to the lobule of the auricle, by union of the posterior division of the retromandibular vein and the posterior auricular vein. The external jugular vein crosses the sternocleidomastoid muscle in the superficial fascia and then pierces the fascia roof of the posterior triangle at he posterior boarder of the sternocleidomastoid muscle. It then passes obliquely through the inferior part of the posterior triangle to empty in the subclavian vein 2cm superior to the clavicle. 


A raised JVP in heart failure may be seen throughout the course of the external jugular Vein. A JVP is raised in increased thoracic pressure, obstructed by a tumour, and enlarged supraclavicular lymph nodes. Opera singers have bilateral enlargement of their external jugular veins due to prolonged periods of increased intrathoracic pressure. IV Fluid overload may have a engorged JVP. Laceration of the external jugular about 5cm superior to the clavicle, may result in air embolism as the External Jugular can not retract when it pierces the deep fascia of the posterior triangle - the patient may present with dyspnea and cyanosis.

Vein: External jugular vein
Veins of the head and neck. (External jugular visible at center.)
Veins
Latin	vena jugularis externa
Gray's	subject #168 646
Drains from	cranium, face
Source	posterior facial vein,posterior auricular vein,anterior jugular vein
Drains to	subclavian vein
MeSH	Jugular+Veins

Anatomy: The Neck, anatomy, Posterior Triangle of the Neck

Arteries of the Posterior Triangle of the Neck

The third part of the subclavian artery. The subclavian artery has 3 parts - separated by the scalenus anterior in thirds - the last third is the part between the scalenus anterior and the clavicle. It is a fingerbreath superior to the clavicle.

The transverse cervical artery arises from the thyrocervical trunk - a branch of the subclavian artery. The transverse cervical artery runs superficially and laterally across the posterior triangle, 2 to 3 cm superior to the clavicle.

The Suprascapular artery from the branch of the thyrocervical trunk - runs posterior to the clavical to the muscles around the scapula.

Artery: Transverse cervical artery
Superficial dissection of the right side of the neck, showing the carotid and subclavian arteries. Transverse cervical artery is labeled, branching from the thyrocervical_trunk.
Superficial and deep branches from the transverse cervical artery.
Latin	arteria transversa cervicis, arteria transversa colli
Gray's	subject #148 82
Supplies	Trapezius Sternocleidomastoid
Source	Thyrocervical trunk
Branches	Superficial branch Deep branch
Vein	Transverse cervical veins

Occipital artery is a branch of the external carotid artery enters the apex of the posterior triangle before ascending to the occipital area. 

Nerves in the posterior triangle. The Accessory nerve (CN XI) that divides the posterior triangle into a superior and inferior parts. The Accessory nerve is a motor nerve consisting of spinal (C1 to C5) and cranial roots. The spinal roots travel superiorly and enter the posterior cranial fossa through the foramen magnum. Here they join the cranial roots of the accessory nerve from the Medulla. Both combined roots leave the skull through the jugular foramen.

The Spinal roots separates immediately and supplies the Sternocleidomastoid muscle and the trapezius muscle.

Lesions to the Accessory Muscle are rare. The Accessory Nerve may be damaged by Traumatic injury, tumours to the base of the skull, fractures involving the jugular foramen, and neck lacerations. Presents with weakness in turning the head to the OPPOSITE site against resistance. Unilateral paralysis of the trapezius muscle is evident by the patients inability to elevate and retract the shoulder, and is unable to lift the arm above the horizontal level. Drooping of the shoulder is obvious.


The Accessory Nerve function can also be functionally impaired by inflamed lymph nodes in the neck. During surgical dissection of the neck lymph nodes care should be taken to isolate and preserve the  Accessory Nerve. 

Nerve: Accessory nerve
Plan of upper portions of glossopharyngeal, vagus, and accessory nerves.
Inferior view of the human brain, with the cranial nerves labelled.
Latin	nervus accessorius
Gray's	subject #206 913
Innervates	sternocleidomastoid muscle, trapezius muscle
MeSH	Accessory+Nerve

The Cervical Plexus


, Anterior triangle, Arteries, Carotid Artery, Carotid Body, , Hyoid Muscles, Muscles, Neck, Nerves, , Posterior triangle, raised JVP, , XI