PRIMORDIAL CRANIUM OF THE CAT 347 



records the presence in the calf of a connective tissue layer 

 dorsad of the chorda. Weiss ('01) found, in embryos of the 

 white rat, an exceptional development of the perichordal sheath 

 in the occipital region, not separated from the horizontal plate 

 of the primitive arch of the atlas (p. 511). The work of Gaupp 

 ('06) on Echidna, and Weigner ('12) on man, support the view, 

 first brought forward by Weiss, of a special development of 

 perichordal tissue about the occipital notochord in mammalian 

 embryos. Weiss described the notochord as occupying, in the 

 blastemal stage, a position at the dorsal surface of the segmented 

 portion of the floor of the occipital region; he found that the 

 cranial end of the perichordal sheath grew to assmne a globular 

 form; in the chondral stage, cartilage appeared in the perinoto- 

 chordal sheath, quite independently of the process of chondrifica- 

 tion which takes place lateral to and beneath the notochord in 

 the formation of the lateral occipital arches and the basal plate. 

 The more or less spherical cartilage so formed about the noto- 

 chord is fused, in later stages of development, with the carti- 

 laginous centrum of the atlas, and becomes eventually the ex- 

 tremity of the dens epistrophei. Weiss saw in the cartilage 

 forming the end of the dens epistrophei, which is marked off 

 from the cartilaginous centrum of the atlas by grooves, an ele- 

 ment comparable with a vertebral centrum, and concluded that 

 it represented the body of an occipital vertebra, or of a proatlas. 

 Gaupp ('06) found the dens epistrophei in Echidna embryos to 

 be composed of the centrum of the atlas and, in addition, of 

 material lying cephalad (and perhaps derived from the basis 

 cranii). This author is of the opinion that the dens epistrophei 

 and the ligamentum apicis dentis represent the anterior reduced 

 end of the vertebral column in which a number of vertebral 

 centra lie imbedded. Weigner ('11) found in a human embryo of 

 13.5 mm. paired anlagen in the floor of the occipital region, pre- 

 senting a notch laterally for the hypoglossal nerve, with a deep 

 groove between their caudal extremities occupied by mesen- 

 chyma, in which the notochord lies. In the ventral part of this 

 sheet, the hypochordal arch of the occipital region was observed. 

 In the atlantal region, in the tissue dorsad of the notochord, the 



