THE ABDOMEN, EXTERIOR. 443 



abdominal wall. How these coverings are secured is ex- 

 plained later ; only their names can be given now. First is 

 the dartos, as already described. Second, the external sper- 

 matic fascia. Third, the cremasteric fascia. Fourth, the 

 infundibuliform fascia. Fifth, the extraperitoneal tissue. 

 In addition to these the testicle has a partial envelope formed 

 of peritoneum, called the tunica vaginalis. 



Of these various layers only the first, third, and last can 

 be demonstrated apart from their sources. For the first, 

 see page 406 ; for the second, page 460 ; the last, the tunica 

 vaginalis, is a covering the testicle has acquired from the 

 peritoneum, see page 460. It consists of two layers ; the 

 visceral, enveloping the testicle, except at its posterior 

 part ; and the parietal, forming the walls of the sac contain- 

 ing the gland. 



DISSECTION. 



Open the tunica vaginalis and recognize the following parts ; The testicle 

 proper and the epididymis. 



The tunica albug-inea (Fig. 93) is the dense white 

 fibrous covering of the testicle. At the posterior margin of 

 the testicle there is an extension from this capsule into the 

 body of the gland of a fibrous septum called the mediasti- 

 num, from which radiate secondary septa dividing the organ 

 into lobes. 



The epididymis lies at the back of the testicle and is 

 divided into the head or globus major, the body, and the 

 tail or globus minor, from which the vas deferens extends. 

 See page 542. 



Obliquus Externus Abdominis. Fig. 89. 



Origin. From the outer surface and lower margin of 

 the eight lower ribs, by muscular slips that interdigitate, 

 the three lower ones with the latissimus dorsi, the rest with 

 the serratus magnus. 



