336 CHARLES CLIFFORD MACKLIN 



does not present this foramen the cartilage in this locality is very 

 thin. The foramen contains nothing but loose connective tissue 

 and its direction is from within downwards and forwards. It 

 may be known as the paracondyloid foramen, and appears in the 

 model of Hertwig on the right side only. 



The squamous portions form the dorsal, and most of the lateral, 

 part of the occipital ring. The architectural, and, as we shall 

 later see, possibly the developmental foundation of each half, 

 is the crescentic bar of cartilage which forms the lateral bound- 

 ary of the primitive foramen magnum, and extends between 

 its two prominences (figs. 1, 2 and 5). Rounded in cross-section 

 it is seen to diminish in size gradually and uniformly from before 

 backwards. Ventrally it is directly continuous with the condy- 

 loid portion (and may even be looked upon as a backward ex- 

 tension of this), the area of union being marked by the anlage of 

 the future condyle, which has been termed the ventral foraminal 

 prominence. Its principal direction is dorsal and slightly cranial, 

 in contrast to that of the condylar portion, which, as has been 

 noted, is caudal, lateral and slightly dorsal. Its concavity looks 

 medially and slightly caudally, the latter curvature being evi- 

 dent when the skull is regarded from the side (fig. 3). Dorsally 

 it terminates in the paired dorsal foraminal prominences, which 

 mark the entrances into the incisura occipitalis superior. As 

 will be seen later this bar corresponds to the neural arch of the 

 occipital vertebra, and will he hereafter referred to as such. 

 Medial to it is the anlage of the future medulla oblongata. Just 

 above its ventral portion appears the jugular tubercle, and, upon 

 examining the cartilage in this location, the cells are seen to pre- 

 sent, from the dorsal part of this tubercle to a point about midway 

 between the foraminal prominences, a condition similar to that 

 which obtains in the central part of the basilar portion. This 

 would seem to point to the beginning endochondral ossification 

 of the ex-occipital portion of the occipital bone, the center for 

 which, according to Mall ('06) appears on the 56th day. The 

 ventral part of this center is confined to the jugular tubercle, but, 

 as the sections are followed backward, it is found that it gradually 

 comes to involve the entire core of the neural arch. The involve- 



