80 TOPOGRAPHICAL ANATOMY OF THE 



coccygeal vertebrae. These soon become so closely applied to each other 

 as to form apparently a single muscle, vi. retractor penis, that can be 

 traced along the urethral border of the penis to within a short distance 

 of the glans, where it disappears under the bulbo-cavernous muscle. 



A. OBTURATORIA. — Blood is supplied to the penis by three arteries 

 on each side of the body. (1) The external pudendal artery has already 

 been examined (page 76). (2) The internal pudendal artery will be ex- 

 amined along with the contents of the pelvis. (3) The obturator artery 

 appears in the present dissection between the gracilis and semi- 

 membranosus muscles and furnishes numerous branches to the penis in 

 the neighbourhood of the root. One of these anastomoses with the 

 internal pudendal artery, and not infrequently a similar union is 

 effected with the caudal branch of the external pudendal artery. 



The obturator vein (v. obturatoria) accompanies the artery. 



Nn. dorsales penis. — The dorsal nerves of the penis are derived 

 from the right and left pudendal nerves, and reach the penis by 

 bending round the sciatic arch. Each dorsal nerve will be found 

 following the margin of the dorsum of the penis in company with and 

 lateral to a dorsal artery. 



Dissection. — In order that the internal structure of the penis may be 

 studied, sections should be made across the organ at different levels. 

 Thus an adequate understanding of the arrangement of the cavernous 

 bodies and the urethra may be arrived at. 



The thick albugineous coat of the corpus cavernosum penis is very 

 obvious, and there will be no difficulty in recognising bi'anching and 

 anastomosing fibrous trabeculae, connected with the tunica albuginea 

 and supporting the erectile tissue of which the body is composed. The 

 erectile tissue itself consists of thin strands between which are 

 cavernous spaces (cavernae) that must be regarded as taking the place 

 of capillary vessels between the arteries and the veins. 



The corpus cavernosum urethras has a similar structure, but its 

 trabeculse are much finer and the cavernae are greatly more spacious. 

 In the glans penis the cavernse are still larger, and, because of the high 

 elasticity of the trabeculae, are very distensible. 



The dissector will now turn his attention to the wall of the 

 abdomen. 



M. CUTANEUS. — The cutaneous muscle covers a considerable extent 

 of the abdominal wall. Thickest over the lateral aspect of the thorax 

 and abdomen, it gradually thins towards the mid-ventral line and 

 merges into the superficial fascia of the ventral wall of the abdomen. 

 It will be noted that some fibres of the muscle are continued into the 

 conspicuous and sharp fold of skin that connects the distal part of the 

 thigh with the abdominal wall. 



V. THORACICA EXTERNA. — The external thoracic vein drains the 

 surface of the lateral and ventral parts of the abdominal wall, some of 



