Common Frog. 37 



at a point between the liver and the duodenum. The terminal 

 and proximal segments of the digestive tracts are thus brought, 

 as is usual in vertebrata, into close apposition °. On the dorsal 

 surface^ and immediately behind the tip of the coccygeal style, 

 is seen the anus. From the tip of the coccyx a slender muscle, 

 the pyriformis, passes outwards to be inserted into the femur, 

 and in the angle between it and the coccyx anteriorly and in- 

 ternally, We see the posterior lymphatic heart. 



The cerebral ganglia form elongated ovoidal masses separated, 

 from each other by a median fissure, and by a slight constriction 

 from the olfactory lobes which are fused mesially with each other. 

 The cerebral ovoids have their anterior extremities converging 

 and their posterior extremities diverging, whilst the anterior ex- 

 tremities of the somewhat similarly shaped but much smaller 

 corpora bigemina, or ' optic lobes,"" homologous with the corpora 

 quadrigemina of mammals, diverge, and the posterior are in mutual 

 apposition. An irregularly diamond-shaped space is thus marked 

 out between these two divisions of the encephalon ; and in it we 

 see the vascular pineal gland and the homologues of the ' optic 

 thalami.' Posteriorly to the optic lobes, and interposed between 

 them and the triangular ^fourth ventricle^ formed by the diver- 

 gence of the strands of the spinal cord, we see a thin transverse 

 lamina of nerve-substance, the homologue of the cerebellum. 



Good figures and detailed descriptions of various organs and 

 systems in this creature will be found in Professor Ecker^s 

 Icones Physiologicae. See, for the circulatory system, Taf. iv., 

 for the lymphatic system, Taf. v., for a history of the develop- 

 ment, Taf. xxiii., and for the nervous system, Taf. xxiv. For 

 a detailed account of the venous system generally, see Gruby, 

 Ann. Sciences Naturelles, Ser. ii., tom. xvii., 1842; and for 

 one of the renal portal system, see M. Jourdain, Ann. Sci. Nat. 

 Ser. iv., tom. xii. 1859, whose very valuable paper appeared 

 subsequently to the third volume of M. Milne-Edwards' Le9ons 

 sur la Physiologic, but has had its conclusions endorsed by 

 that authority in his vol. vii. p. 349, 1862. 



For the tegumentary system with its muco-nervous organs, see 

 Leydig, Nova Acta, 1868, p. 62. 



o See Duvernoy in Cuvier's Le9ons d'Anatomie Comparde, tom. iv. pt. ii. p. 657. 



