56 MAMMALIA. 



only a pair of lateral tegumentary folds), within which are situated the 

 mammae and nipples, to which the still slightly developed embryos 

 attach themselves, and are there completely formed. The pouch is 

 a duplicature of the external integument, which posteriorly and supe- 

 riorly stands in connexion with the tendon of the external oblique 

 muscle of the abdomen. The muscle of the mammary gland, al- 

 ready mentioned (compressor mamma), is situated upon the external 

 oblique muscle, arises from the posterior part of the pelvis, becomes 

 broader anteriorly, and divides into two slips, between which the 

 nipples are enclosed. The number of the latter is greater in the 

 carnivorous than in the herbivorous Marsupiata. 



The Male sexual organs, like the female, exhibit considerable di- 

 versities in the several orders. The Testicles, as in Man, are oval 

 or rounded, and sometimes much elongated and thin or slender, as 

 in the Cetacea. They have a tunica vaginalis, but are seldom sit- 

 uated, as in Man, in a scrotum separated by a partition, this being 

 the case only in the Apes, several Carnivora, the Ruminantia, and 

 the Horse. The scrotum usually stands in communication with the 

 abdominal cavity through an open inguinal canal. In many insectiv- 

 orous Carnivora and in most Rodentia, the scrotum is all but want- 

 ing, and the testicles lie in the perineum, as in the Beaver, or within 

 the abdominal cavity, as in Sorex, Erinaceus, Talpa, Myoxus, and 

 many others, while in other genera and in the Cheiroptera the tes- 

 ticles, during the rut at least, glide back into the belly. In the Ce- 

 tacea and Monotremata, as also in some Pachydermata, e. g. the 

 Elephant, and indeed, in many Rodentia, the testicles are situated 

 permanently in the abdomen, upon either side of the rectum, and are 

 there retained in their place by a mesentery similar to the broad lig- 

 aments of the uterus. The internal structural arrangement of the 

 testicle is essentially the same as in Man ; the delicate seminifer- 

 ous tubes uniting into the seminal duct form an epidydymis. In 

 many animals a portion of the tunica albuginea is given off as a strip 

 of various form, which sends laterally ray-shaped fibres between the 

 lobules of the seminal vessels ; this structure is known by the name 

 of Corpus Highmori, and is particularly distinct in the Ruminantia, 

 and also in the Horse and Dog. At the spot where the vasa defer- 

 entia unite, before the commencement of the urethra, they form not 

 unfrequently an expansion like the uterus, or a kind of sinus, which 

 is perhaps to be viewed as a remnant of the sinus urogenitalis in the 

 foetus. 



The testes secrete a white Semen, the moving elements of which, 



