Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/811

Rh AMPHIBIA 767 domraal cavity, and clearly represents the Wolffian duct of the embryo. Both the urinary tubuli and the vasa e/erentia of the testis open into this duct. In Crypto- branchus the kidney is divided by a constriction into two portions a slender, anterior, and a much thicker and longer, posterior, division. From the latter the efferent urinary canals proceed, and, curving outwards and back wards, join the posterior part of the Wolffian duct. The former is traversed by the vasa eferentia of the testes, which pass from its outer edge to the anterior portion of the WoLffian duct, so that it resembles an epididymis. 1 In Proteus, according to Leydig, the anterior end of the Wolffian duct is infundibuliform and open ; the vasa e/er entia of the testes open into the anterior moiety of the duct, the renal ducts, into its posterior moiety. The numerous arcuated renal ducts of the Salamanders and Tritons unite together, and open into the Wolffian duct near its cloacal end. The Wolffian duct persists in Bombinator igneus and Disco- glossiis pictiis 2 ; but, in most Anura, it becomes obliterated for the greater part of its extent, and the same canals serve to convey both the urinary and the spermatic fluids to the persistent cloacal end of the Wolffian duct, which ordinarily receives the name of ureter. The urinary bladder is always large, and is often bifurcated anteriorly. The Nervous System. The amphibian brain is remark able for the rudimentary condition of the cerebellum, which has the form of a mere band arching over the anterior part of the fourth ventricle. The mesencephalon is divided above, more or less distinctly, into two optic lobes. The cerebral hemispheres are always relatively large, subcylin- drical in the Urodela, but wider behind than in front in the Anura, and they are generally closely united together by their inner faces. Fio. 26. Diagram of the chief cranial nerves of Rana esculenta. II. optic ; IV. pathetic; V, orhito-nasal ; V 2, superior maxillary; V 3 , inferior maxillary; Vila. VIIp. anterior and posterior divisions of the portio dura; IX. the glosso-pharyngeal ; X. the pneumojrastric ; X, its dorsal branch. Sp. I. The iirst spinal nerve (hypoglossal). 01. olfactory nerve; Tg. tongue; lly. cornu of the liyoid ; lid. llavderian gland. Ten pairs of cranial nerves are always found-&quot; viz., 1, The olfactory; 2, optic; 3, oculomotor; 4, pathetic; 5, trigeminal; 6, abducens; 7, portio dura; 8, auditory; 9, glossopharyngeal ; 10, pneumogastric. The hypoglossal is always an extra- cranial nerve. 1. The olfactory is usually a rounded cord, not dilated at its anterior end. Fischer has observed it to arise by two roots in Pipa. 2. The optic nerves are attached, as usual, to the floor of the thalamencephalon. Fischer 3 found no chiasma in Siredon or Menobranchus. Dr Humphrey found none in 1 Schmidt, Goddard, and Van der Hoeven, Aantcekningen over de Anatomic van den Cryptobranchus japonicus. 2 According to Von Wittich. &quot; Beitrage zur morphologisclien und his- tologischen Entwickelung der Harn und Geschlechtswerkzeuge der nack- ten Amphibien,&quot; Zeitschrift fur Wissenschaftliche Zoologie, bd. iv. 3 Anatomische Abhandlungen, p. 123, ctseq. Cryptobranchus ; but sections of the brain are needful before the actual absence of the chiasma can be considered to be satisfactorily proved. 3. The oculomotor nerve remains distinct from the trigeminal in most Amphibia, but its branch to the superior rectus muscle appears to coalesce with the orbito-nasal division of the fifth in Salamandra terrcstris (Fischer). 4. The pathetic nerve remains distinct in Siredon and Cryptobranchus, and in the Anura; but in Salamandra ter- restris, Fischer found that the superior oblique muscle was supplied by a branch from the orbito-nasal, with which, therefore, the pathetic had probably coalesced. 5. The trigeminal gives rise, as usual, to a Gasserian ganglion ; and this ganglion remains distinct from that of the seventh nerve in all the Urodela, though united with, it by a commissural band, which appears to answer to the nervus petrosus superftcialis minor of the higher Vertebrata. In the Anura, on the contrary, the two ganglia are closely approximated (Pelobates, BombinatorY, or confounded together (Rana, Hyla, Bufo) in the adult, though they are distinct in the tadpole. The orbito-nasal, or first division of the trigeminal, is always separated from the second and third divisions by the ascending process of the suspen- sorium, when this structure is present. It supplies the tentacles of the Peromela. In the tadpole, and in some Urodela, a cutaneous branch to the dorsum of the head is given off from the fifth. 6. The abducens is distinct from the trigeminal in Sala mandra and Bufo, but coalesces with the Gasserian gan glion in Rana, Pipa, and most Anura. 1 and 8. The portio dura and portio mollis arise by a common trunk, from which the portio dura soon separates, and either forms a distinct ganglion, as in the Urodela and Peromela, or fuses with the trigeminaL 9. The ganglion of the glossopharyngeal nerve appears to coalesce with that of the vagus, and the roots of the two nerves pass out of the same foramen in all the Amphibia, except Siren, where, according to Fischer (op. cit., p. 147), the nerve leaves the skull by a distinct aperture, close in front of that for the pneumogastric, and forms a ganglion of its own. 10. The vagus or pneumogastric, in the perennibranchiate Amphibia, supplies the second and third branchia, and the cucullaris muscle ; gives off cutaneous, laryngeal, cardiac, pulrnonic, and gastric branches, and sometimes as many as three cutaneous branches, one of which runs along the junction of the dorsal and ventral muscles to the hinder part of the body. These lateral nerves of the pneumo gastric exist also in Menopoma, Amphiuma, and Triton, and in tadpoles ; but appear to be absent in Salamandra ter- restris and in the adult Anura (Fischer, I.e.) These, however, possess a cutaneous branch of the vagus, which accompanies the cutaneous branch of the pulmo-cutaneous artery, and is distributed more or less widely to the dorsal integument of the head and trunk. Fischer considers that a fine nerve, arising lower down than the vagus, and distributed to the abductors of the head in Pipa., is to be regarded as an accessorius. But, seeing that, in the Amphibia generally, the motor nerves of the larynx, and, where a cucullaris exists, the nerves of that muscle also, are supplied from the pneumogastric, the question of the presence or absence of an accessorius seems to reduce itself to this : Does the pneumogastric receive nerve fibres arising from the sides of the medulla ollongata and spinal cord between the roots of the spinal nerves ] And, as it certainly does not, the accessorius, as it exists in the higher Vertebrata, must be admitted to be absent in Amphibia. In most Amphibia, the first cervical nerve has the dis- 4 According to Stannius, Handbuch, p. 150.