332 



ZOOLOGY 



SECT. 



mn 



the position of which has been ah-eady mentioned. It communicates 

 with the cavity of the mouth by the Eustachian passage, which is 

 narrower and longer than in the Frog. The inner wall of the 

 tympanic cavity is formed by the bony wall of the auditory region 

 of the skull, in which there are two fenestrse — the fenestra ovalis 

 and the fenestra rotunda. The columella stretches across the 

 cavity from the tympanic membrane, and is fixed internally into 

 the membrane covering over the fenestra ovalis. 



The parts of the membranous labyrinth (Fig. 974) are enclosed 

 by the bones of the auditory region : between the membranous 

 wall of the labyrinth and the surrounding bone is a, small space 

 _ containing fluid, the fi^i">'- 



lymfh. The labyrinth itself 

 consists of the iitrieidus 

 with the three semicircular 

 canals and the sacculus with 

 the lagena (cochlea). The 

 utriculus {ii.) is a cylindrical 

 tube, bent round at a sharp 

 angle : the semicircular can- 

 cels (ccL, ce., cp.) are arranged 

 as in Vertebrates in 

 general (p. 115). A narrow 

 tube, the ductus endolympha- 

 ticus, leads upwards towards 

 the roof of the skull and ends 

 blindly in the dura mater. 

 The sacculus is large and 

 rounded. The lagena (l.) 

 forms a flattened, not very 

 proininent, lobe, and is of 

 simple form. 



Urinary and Reproductive Systems. — The kidneys (Figs. 

 975 and 976, Jc.) are a pair of irregularly shaped, dark red bodies, 

 each consisting of two lobes, anterior and posterior, situated in 

 close contact with the dorsal wall of the posterior portion of the 

 abdominal cavity, and covered with peritoneum on their ventral 

 faces only. Their posterior portions, which are tapering, are in close 

 contact with one another. Each h.^s a delicate duct, the ureter, open- 

 ing posteriorly into the cloaca. A urinary (allantoic) bladder (hi), 

 a thin-walled sac, opens into the cloaca on its ventral side. 



In the male the testes (Fig. 975, if.) are two oval white bodies, 

 that on the right side situated just posterior to the right lobe of 

 the liver, that on the left somewhat further back. Each testis is 

 attached to the body-wall by a fold of the peritoneum, the mes- 

 orchium (ms. o.). The epididymis (ep.) extends backwards from the 

 inner side of each testis, and passes behind into a narrow convoluted 



Fio. 074.— Membranous labyrinth of Iiacerta 

 TiridiS) viewed from the outer side. act. an- 



terif.r ampulla ; ac. auditory nerve ; ade. opening 

 of the ductus endolymphaticus ; ae. external 

 ampulla ; ap. posterior ampulla ; hr. basilar 

 branch of nerve ; ca. anterior semicircular canal ; 

 ce. external semicircular canal ; cp. posterior 

 semicircular canal ;c.u8. canal connecting utriculus 

 and sacculus ; de. ductus endolymphaticus ; I. 

 lagena ; mb. basilar membrane ; raa, rae, rap. rl. 

 branches of aud.tory nerve ; s. sacculus ; ss. com- 

 mon canal of communication between anterior 

 and posterior semicircular canals and utricle ; 

 u. utriculus. (From Wiedershoim's Comi^arative 

 Anatomy, after Retzius.). 



