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 vertebra? 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 higheTTrimates the tail forms a stump-like appendage, 

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

 however, the aiotochord 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 vertebra? 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 vertebrse 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. 



BIBLIOGRAPHY. 



AGASSIZ, L. Rech. sur Us poissoiisfossiles. Neuchatel, 1833 to 1843. 



CARTIER, 0. Beitr. sur Entw.-Gcschiclde der Wirbelsdulc. Zeitschr. f. wiss. Zool. 



Bd. XXV. Suppl. 1875. 

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



1884. (Monograph on Archceopteryx.) 



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

 FOL, H. Sur la queue de Vembryonhumain. Comptes rcndus, 1885. 

 GEGENBAUR, C. Unters. z. vergl. Anatomic der JFirbelsaule der Amphibien und 



Rcptilicn. Leipzig, 1862. Beitr. zur Kcnntniss des Beckens der Vogcl, &c. 



Jenaische Zeitschr. Bd. VI. 

 GERLACH, L. Ein Fall von Schwanzbildung bei eincm mcnschl. Embryo. Morphol. 



Jahrb. Bd. VI. 

 GOTTE, A. Beitr. zur vergl. Morphologic des Skeletsystems der Wirbclthicre. Arch. 



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

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



London, 1871. 



HASSE, C. Das natiirl. System der Elasmobranchier, <&c. Jena, 1879-82. 

 HOFFMANN, C. K. Beitr. z. vergl. Anatomie der Wirbelthiere. Nicderl. Arch. /. 



Zool. Bd. IV. 

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



America. "Washington, 1880. 

 MAYER, P. Die unpaaren Flosscn der Selachier. Mittheilungen der Zoolog. Station 



zu Neapel. 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 Selacliicr-schadcls. Dorpat, 1884. 



Ufbcr die Entwicklung der Wirbelsdule und das Centrale carpi des Mcnschen. 



Morphol. Jahrb. Bd. I. 1876. 



