348 CHARLES CLIFFORD MACKLIN 



My identification of the primitive elements forming the pars 

 basilaris also is not exactly in agreement with Levi's, but the 

 difference depends largely on where the line between the basilar 

 and lateral portions of the occipital anlage is drawn. 1 have as- 

 sumed the separation between these portions to be approximately 

 as it exists at birth, while Levi includes in his lateral portions the 

 nodules which I believe represent the paired body of the occipital 

 vertebra. If my interpretation of these structures is correct 

 they should be regarded as constituents of the basilar portion, 

 which would thus represent the body masses of the undifferentiated 

 sclerotomes plus the body mass of the occipital vertebra, while 

 according to Levi's view it would represent only the body masses 

 of the undifferentiated vertebrae. 



In the later development of the chondrogenous stage the 

 forerunners of the individual features of the occipital bone begin 

 to show themselves, and we find cartilaginous representatives 

 of the body, pedicles, inferior and superior articular processes, 

 transverse (and possibly costal) processes, laminae and spinous 

 processes, these almost altogether differentiating from the occipi- 

 tal scleromere. The development of the body (pars basilaris) 

 has already been discussed. The pedicles are, of course, rep- 

 resented by the cartilaginous tissue in the region of the hypo- 

 glossal foramen, but here we have material added from the 

 lateral mass of the cranial sclerotomes, (Froriep, Levi), which 

 results sometimes in the partitioning of the foramen, as may be 

 seen on the left side of my model, and as has frequently been 

 found by other observers in young embryos of homo and other 

 mammals. The inferior articular process is, doubtless, repre- 

 sented by what has been designated the ventral foraminal prom- 

 inence, the forerunner of the condyle, though the condyle of 

 the mature bone is partly formed by the pars basilaris. The 

 rudiment of the superior articular process is, perhaps, to be seen 

 in the jugular tubercle. The transverse process, as we have 

 seen, is to be found in the paracondyloid process, and there is 

 some evidence to indicate that in this latter there may be in- 

 cluded the costal process as well. It will be remembered that 

 the paracondyloid process was perforated on the left side by 



