AMNIOTA: MAMMALIA. 359 



1881 ; ii. 1884; (abstracts in Biol. Centralblatt, ii. 1882-85 ; v. 1885-86). Middle 

 and external ear, Moldenhauer, M. J. iii. 1878. Bones of Ear in the Mammalia, 

 W. K. Parker, 'Mammalian Descent,' Hunterian Lectures, 1884, p. 39. 



Comparative anatomy of Tongue, Ludwig Ferdinand, Konigler Prinz von 

 Bayern, Miinchen, 1884. 



Thymus and Thyroid, development, Fischelis, A. M. A. xxv. 1885 ; cf. Dohrn, 

 Mitth. Zool. Stat. Naples, vi. 1885. 



Blood corpuscles of Vertebrata, Gulliver, P. Z. S. 1875. 



Cloaca, &c., Spoof, Embryol. u. Vergleich. Anat. der Kloake u. der Uro- 

 genital-system bei den hoheren Wirbelthieren, Helsingfors, 1883. 



Development of organs in general, Balfour, Comparative Embryology, ii. 1881, 

 Chapters on Organogeny; Foster and Balfour, ' Embryology of Chick,' ed. 2, by 

 Sedgwick and Heape, London, 1883. 



AMNIOTA s. Allantoidea s. Abranchial a. 



THE embryo is provided with the two foetal envelopes known as the 

 amnion and allantois. Branchiae are never developed. 



Three classes are included in this division of Vertebrata, the Mam- 

 malia, Aves and Reptilia. The two latter are very closely connected in 

 descent, and may be grouped together as Sauropsida. 



CLASS MAMMALIA. 



Air-breathing -warm-blooded Vertebrata in -which the epidermis de- 

 velopes hairs over a greater or less extent of the surface of the body : which 

 are viviparous with the exception of Prototheria, and always nourish their 

 young for longer or shorter periods after birth with the secretion of lacteal or 

 mammary glands. There are two occipital condyles to the skull and seven 

 cervical vertebrae. The coelome is divided into a thoracic and abdominal 

 portion by a muscular diaphragm. The aorta is single and bends over the 

 left bronchus ; and the red corpuscles or haematids are non-nucleated. The 

 rectal and urogenital apertures are typically separate, and the former placed 

 behind the latter. 



The minute structure and the character of the hairs vary much in 

 different Mammals, and on different parts of the body in the same Mammal. 

 The hairy coat is scanty in some instances, e. g. Sirenia, Hippopotamus ; and 

 in Cetacea is restricted to the snout, where it may be present only in the 

 foetus. The edges of the eyelids are protected by a single row of hairs 

 the eye-lashes or cilia : and the snout in most Mammalia has a few stout 

 tactile hairs, or vibrissae, connected with an abundant nerve-supply. Certain 

 hairs, e. g., those of the mane and tail in Equidae, the vibrissae, appear to 

 be persistent, but as a rule the coat is shed both before and after the winter 

 season : the winter coat being thicker and sometimes, as in Arctic Mam- 



