FOEM OF THE EODY OF VEETEBEATA. 413 



Todd's Cyclopaedia. I. — Milne-Edwards, ALPH.,-Recli. sur les ossemens fossiles dcs oiseaux 

 Paris, 1806.— Alix, E., Appareil locomotcur des oiseaux. Paris, 1374. 



Mammalia : Meckel, J. Fr., Omithorhyncbi paradoxi descriptio anatomica. Lips. 182G.— Veolik 

 (Dendrolagus), Verbandel. d. Kon. Acad. Amsterd. V.— Guklt, Handb. d. vergl. Anat. dcr 

 Haussiiugethiere. 4 Aufl. Berlin, I860.— Fbanck, L., Anatomie der Hausthiere. Stuttgart, 1871. 

 — Brandt (Lama), M^m. Acad. St. Petersbourg, 1841.— Owen (Giraffe), Transact. Zool. Soc. II.— 

 The same (Rhinoceros), Transact. Zool. Soc. IV. n.— Milne-Edwabds, Alph. (Moschiaxl), Ann. 

 sc. nat. V. ii.— Murie, J. (Manatus). Tr. Zool. Soc. VIII.— Camper, Observations sur la structure 

 intime et le squelette de Cetac6es. Paris, 1820.— Rapp, Die Cetaceen. Stuttgart u. Tubingen, 

 1837. — Vrolik, W., Natuur- en ontleedkund. Beschouwing van d. Hyperoodon. Haarlem, 1848. 

 Eschricht, Untersucb. iiber die nordischen Waltbiere. Leipzig, 1849.— Murie, J. (Globio- 

 cephalus, Otaria, Trichechus), Tr. Zool. Soc. VII. VIII.— Rapp, Anatom. Untersucbungen iiber 

 die Edentaten. 2 Aufl. Tubingen, 1852.— Owen (Myrmecophaga jubata), Tr. Zool. Soc. IV.— 

 Hybtl (Chlamydopborus truncatus), Denkschr. d. Wien. Acad. IX. 1855.— Pouchet, G., M<?m. 

 sur le grand Fourmilier. Paris, 1874.— Pallas, Nov. spec, quadrup. e glirium ordine. Erlangen, 

 1778.— Camper, Descript. anat. d'un Elephant male. Paris, 1802. — Burmeister, Beitriige z. 

 nahern Kentniss der Gattung Tarsius. Berlin, 1846.— Van der Hoeven (Stenops), Verband. d. 

 Acad. Amst. VIII.— Owen, Monograph on the Aye-Aye. London, 1863.— Peters (Cbiromys), 

 Abhandl. d. BerUner Acad. 1865.— Murie, J. (Lemuridse), Tr. Zool. Soc. VII.— Tyson, Anatomy 

 of a Pygmy. London, Sec. edit. 1751. — Vrolik, Rech. d'anat. comp. sur le Chimpanse. Amster- 

 dam, i841.— Duvebnoy, G. L., Caract. anat. des grands singes. Archives du Museum. VIII.— 

 Flower, Osteology of the Mammalia. London, 1870.— Turner, W., Lectures on comp. anat. of 

 the Placenta. Edinburgh, 1876.— For hitman anatomy, reference must be made to the manuals on 

 the subject. 



Form of the Body. 

 § 316. 



The external metamerism disappears, but dorsal and ventral 

 surfaces can generally be distinguished; the entrance into the 

 nutrient canal is placed near the anterior pole of the long axis of the 

 body, and on the ventral surface ; the anus is also ventral, but is at 

 some distance from the aboral pole. Three great regions can be 

 made out even in the body of the lowest divisions. The anterior one 

 contains a respiratory chamber formed from the nutrient canal, and 

 is consequently distinguished by clefts in the sides of the body-wall. 

 It carries the higher sensory organs, and in the Craniota gives rise, 

 by concrescence and differentiation, to a head. 



The second portion, which in Amphioxus is not sharply marked 

 off on the dorsal surface from the preceding one, forms the trunk, 

 which encloses the ccelom and its contents ; this is only marked off 

 from the last or caudal portion of the body by the anus ; so that 

 from the outside there is not much difference between them. 



We have already met with these divisions in the Tunicata. In the 

 Ascidian larvas (cf. Fig. 208), the most anterior one, which later on 

 forms the priucipal portion of the body, contains the rudiments of 

 the respiratory cavity, and the portion of the nervous system which 

 contains the sensory organs. Connected with this is a faintly 

 separated tract with the enteric tube, and this passes almost directly 

 into the caudal portion. The earliest characters of the embryonic 

 head, or of its equivalent in all Vertebrata, point to its being, 

 phylogenetically, the most ancient portion of the body, and serve as 

 a finger-post to the path of development of the Vertebrate body. 



With the development of the head and of the organs differen- 

 tiated in and on it, the body of the Vertebrata acquires characters, 

 which, externally, separate it well off from the Invertebrata ; the 

 value of these is clear when we take note of the large number 



