DRINOGENITAL ORGANS, 513 



of the phax'ynx as far as the posterior nares, used exckisively for 

 respiration. A moveable epiglottis (almost tubular in the Ceta- 

 cea), attached to the upper edge of the thyroid cartilage, pro- 

 jects over the glottis. When food is being swallowed it sinks 

 and closes the glottis. Accessory cavities, with membranous 

 or cartilaginous walls, are sometimes attached to the larynx. 

 These sometimes function as air reservoirs, e.g. the air-sacs of 

 Balaena, sometimes as a resonating apparatus for the strength- 

 ening of the voice, as in many monkeys {Mycetes). In many 

 mammals the nasal passages are connected with air-spaces in 

 the bones of the head (frontal, ethmoidal, maxillary bones, etc.), 

 and the tymjDanic cavity communicates with air-sinuses in the 

 mastoid. 



The kidneys (Fig. 268, N) sometimes consist (seals, dolphins) 

 of numerous lobes united together at the pelvis of the kidney. 

 As a rule, however, they are compact bean-shaped glands, lying 

 in the lumbar region, oiitside the peritoneum. The ureters 

 arise from the so-called pelvis of the kidney, and always open, 

 except in Monotremata, into a urinary bladder, placed in front 

 of (ventral to) the intestine. The duct of the bladder joins the 

 ducts of the generative organs, and forms a urogenital canal 

 called vestibule in the female and unethra in the male, opening 

 ventral to the anus. Anterior to the kidneys there is a glandular 

 organ termed the suprarenal body. 



The male sexual organs (Fig. 269) of most Mammalia are 

 characterized by the change in the position of the testes. In only 

 a few cases (Monotremata, Cetacea, etc.) do the testes remain near 

 the kidneys ; in most mammals they descend in front of the pelvis, 

 and, pushing the peritoneum before them, enter the inguinal 

 canal (many rodents), or, still more frequently, pass througli 

 the inguinal canal into a cutaneous fold, which is transformed 

 into the scrotum. Not unfrequently (rodents, bats, insecti- 

 vores) they pass back through the open inguinal canal into the 

 abdominal cavity after the breeding season : this is affected by 

 the cremaster, a slip of muscle separated from the oblique 

 abdominal muscle. The scrotum, as a rule, lies behind the 

 penis ; but in the marsupials it is formed by an invagination of 

 the integument directly at the entrance of the inguinal canal in 

 front of the male copulatory organ. The coiled excretory ducts 

 of the testes, which are derived from the wolffian body and ducts, 



Z.-II. L L 



