Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/810

Rh 766 AMPHIBIA pulmonary artery, and a smaller dorsal cutaneous branch (Hyrtl). The pulmonary artery gives twigs to the stomach. It is clear that the posterior trunk of CryptobrancJms repre sents the second, third, and fourth aortic arches of Salamandra; and that the first aortic arch of Salamandra answers to the first and second trunks which spring from the synangium of Cryptobranchus. In the Anura there are apparently only two aortic arches; but, as has already been observed, each of them is divided into three canals. The anterior canal ends in a rete mirabile, whence the internal carotid artery proceeds, and it gives off the hyomandibular or lingual artery. It therefore answers to the first arch of the Salamanders. The second or middle canal is the largest, and passes into a trunk which runs along the sides of the gullet; and curving backwards, unites with that of the opposite side in the dorsal aorta. The third canal ends in a trunk which divides into the pulmonary and the great cutaneous arteries, which latter is distributed to the dorsal integument. It answers to the third and fourth arches in the Salamanders. Fio. 25. The heart, great arterial trunks, and the adjacent principal nerves of Rana esculenta, drawn to scale. The positions of the auditory capsule (Au.), Eustachian tube (Eu.), nnd hyoidean conm (Hy.), are indicated diagram- matically. L, root of the left lung; S. V. sinus venosus; tf. ventric.e, Au, auricle; TV. A. trancus arteriosus; C.O. carotid gland; Ig. lingual artery; Or. carotid artery; Oph. ophthalmic artery. 2. Left arch of the aorta, pass ing through the muscular diaphragm to the aorta (Ao.) beneath ; tr. in. the transverse process of the third vertebra, br. the brachial artery. 3. Pulmo- cutaneous artery ; ct. its cutaneous, p. its pulmonary division. Nerves: V 1 , V 2, V 3 , first, second, and third divisions of the trigeminal; Vila, VIIjo, anterior and posterior divisions of the portlo dura; IX., the glossopharyngeal ; trunk of the second spinal nerve. In the Peromela (Epicrium) the two aortic trunks which spring from the truncus arteriosus would seem to correspond with the second and third of the frog, the first having become absorbed into the second. This is a point which can be cleared up satisfactorily only by the study of development; but it is obvious that the heart and its arches have undergone greater changes in this group than in any of the others. With respect to the venous system, it is worthy of notice that the blood returning from the hinder part of the body and the pos terior extremities is, in part, carried to the kidneys, and in part poured into a vein which mns in the anterior wall of the abdominal cavity, the anterior abdominal vein. Of the branches in which this vein terminates anteriorly, one communicates with the portal vein, and one is distributed to the liver directly. In the Anura, venous radicles in the ifitegument covering the back of the head and shoulders, unite to form a great cutaneous vein, which passes backwards, perforates the external oblique muscle, and then turn ing abruptly forwards, ends in the subclavian vein. This vein carries away a large part of the blood of the cutaneous artery, which accompanies it in a great part of its course. The lymphatic system has been most carefully studied in the frog, where it consists of (1.) widely-distributed lymphatic capillaries, and sinuses which ensheath the blood-vessels; (2.) subcutaneous lymph sacs; (3.) a large subvertcbral cisterna, enclosed between the diverging lamellae of the mesentery, and placed in communication with the peritoneal cavity by minute openings or stomata; (4.) four lymph hearts, two situated close to the transverse process of the third ver tebra and two at the sides of the coccygeal style. These hearts pump the lymph into the adjacent veins. Aa the two pairs of lymph hearts have been discovered in Triton and Salamandra as well as in liana, it is probable that they are present in the Urodela generally. No Amphibia possess lymphatic glands. The Thynnis gland in the Urodela lies behind the angle of the mandible (Triton, Salamandra), or close to the dorsal ends of the branchial arches (Proteus, Menobranchus, Siredon, Amphiuma, Menopoma). In the Peromela it has the same position as in the abranchiate Urodela. In the tadpole the thymus occupies a place similar to that which it possesses in the branchiate Urodela. In the adult frog it is to be found just behind the suspensorium. The Thyroid gland, usually double, but single (according to Leydig) in Proteus, always lies in the immediate vicinity of tho lingual vessels. 1 The Respiratory Organs. The glottis in the Amphibia is situated in the middle line of the floor of the pharynx. In the perennibranchiate Urodela, it is a very small longi tudinal slit leading into a narrow passage, which widens into a chamber into which the elongated pulmonary sacs open. The Urodela and the Peromela present mere car tilaginous rudiments of a larynx ; but, in the Anura, this structure attains a great development, and becomes the instrument of the powerful voice with which many of these animals are provided. The larynx is lodged in the angle between the two thyro-hyals, with which it is closely con nected. The chief part of the larynx is an annular cricoid cartilage, with which two arytsenoid cartilages are articu lated. Membranous folds, or freely projecting cartilagin ous processes of the arytsenoid cartilages (Pipa), play the part of vocal ligaments. In Pipa the larynx is extensively ossified. In Proteus, the lungs are long tubes, dilated at their posterior blind ends, and fixed to the dorsal walls of the abdominal cavity by folds of the peritoneum. In Triton they are somewhat wider sacs, but, in both, the inner sur faces of the pulmonary sacs are smooth. In Siren and Salamandra, the walls of the sacs become cellular, and in Amphiuma, Henopoma, Cryptobranchus, and the Anura, the cellulation acquires a considerable development. In Amphiuma, Menopoma, Cryptobranchus, and in the Peromela, there is a distinct trachea, which is of great length in the Peromela. In Pipa and Dactylethra there is no trachea, but each lung is connected with the laryngeal cavity by a bronchus. The Renal Organs. The kidney is a more or less elongated organ longer in the Urodela and Peromela, shorter in the Anura which lies on each side of the vertebral column, its posterior end being close to, or even extending back on the dorsal side of, the cloaca. In the female the efferent ducts of each kidney unite into a longer or shorter common trunk, which appears always to open into the cloaca by an aperture distinct from that of the oviduct, though the contrary statement is very generally received. 2 In Rana esculenta, there can be no doubt as to the distinctness of the minute urinary apertures from the large and conspicuous oviducal openings, close to which they are situated. Hyrtl says of Crypto- branchus &quot;Ureter .... super latera cloaca; descendeus in collum allantoidis exoneratur&quot; (op. cit., p. 84). In the male Amphibia, on the other hand, there is a longer or shorter duct common to both the renal and the genital products, which opens into the cloaca. In the Urodela, the duct is continued forwards along the outer side of the kidney to the anterior end of the ab- 1 See Loydig, Anatomisch-histologische Untersuchungcn iibcr Fi-sche und Reptilien, 1853. 2 See, for example, Starmius, Handbuch der Amphibien, pp. 250, 251. On the other side, comp. Milne-Edwards, Lemons, i. vii. p. 336