VERTEBRAL COLUMN. 47 



In Mammals, as in Reptiles and Birds, two primary sacral 

 vertebrae are present, but as a rule a few caudal become later 

 included in the sacrum, and are usually more or less closely united 

 with it. In Anthropoids, as in Man, the first sacral vertebra is 

 plainly marked off from the last lumbar by the appearance of the 

 so-called promontory. 



The caudal vertebrae vary extremely in their development, and 

 excepting in most long-tailed Mammals more particularly the 

 Sirenia and Cetacea no longer develop lower arches. When 

 present these " chevron bones " are intervertebral in position. 



In the higher Primates the tail forms a stump-like appendage, 

 the coccyx consisting of few (3 6) vertebrae. In the embryo, 

 however, the notochord extends beyond the point corresponding 

 to the apex of the coccyx, and thus a longer caudal region must 

 formerly have been present. 



The greatest number of caudal vertebrae is found in Microgale 

 longicauda (48), Manis macrura (46 49), Paradoxurus (about 36), 

 and in certain Monkeys (Semnopithecus, Ateles, 32 33). 



In human embryos of 9 10 millimetres long (5th week) 38 vertebrae are 

 present, and these all consist of a cartilage-like tissue with the exception of 

 the two posterior caudals. In embryos 12mm. long (6th week) the three 

 posterior caudal vertebrae (36th, 37th, and 38th) fuse together, and the 35th 

 also loses its sharp contour. In embryos of 19mm. there are only 34 ver- 

 tebrae, the number present in the adult. In the stage with 38 vertebrae, the 

 spinal cord and notochord extend to the extreme apex of the tail, almost 

 reaching to the skin, but a reduction of these parts takes place later. 



BlBLIOGBAPHT. 



-iz, L. Etch, sur les poissons fossiles. Xeuchatel, 1833 to 1843. 

 CARTIER, 0. Eeitr. zur Entw.-Geschichte der Wirbelsdule. Zeitschr.f. vnss. Zool. 



Bd. XXT. Suppl. 1875. 

 DAMES, "W., and KAISER, E. Palceontol. Abhandlungcn, Bd. II. Heft 3. Berlin, 



1884. (Monograph on Archtzopteryx.) 



FLOWER. W. H. Osteology of the Mammalia. London, 1885. 

 FOL, H. Sur la queue de I'embryonhumain. Comptes rendus, 1885. 

 GEGEXBArR, C. Unters. z. vergl. Anatomic der Wirbclsaulc der Amphibien vnd 



Heptilien. Leipzig, 1862. Beilr. zur Kenntniss des Beckens der VSgcl, dx. 



Jenaische Zeitschr. Bd. VI. 

 GERLACH. L. Ein Fall von Schwanzbildung bei einem menschl. Embryo. Morphol. 



Jahrb. Bd. TI. 

 G-JTTE, A. Betir. zur vergl. Morphologic des Skcletsystems der WirbeUhiere. Arch. 



f. mikr. Anatomic, Bd. XV. 1878. 

 GCXTHER, A. Description of Ceratodus Forsteri. Phil. Trans, of the Royal Society. 



London, 1871. 



. C.Das naturl. System der Elasmobranchier, <bc. Jena, 1879-82. 

 HOFFMAXX, C. K. Beitr. z. vergl. Anatomic der WirbeUhiere. Niederl. Arch. f. 



Zool. Bd. IV. 

 MARSH, 0. C. Odontornithes, a Monograph on the Extinct Toothed Birds of North 



America. Washington, 1880. 

 MATER, P. Die unpaaren Flossen der Sclachier. Mtitheilungen der Zoolog. Station 



apel. Bd. VI. 1885. 

 MIVART. ST. G. On Various Axial Skeletons. Proc. and Trans. Zool. Soc. 1865, 



1869, 1873. 

 ROSENBERG, C. Ueber die Occipital-region des Sclachicr-schadels. Dorpat, 1884. 



Uebcr die Entwicklung far WirbeUaule und das Centralc carpi des Menschen. 



Morphol. Jahrb. Bd. I. 1876. 



