338 . CHARLES CLIFFORD MACKLIN 



by an elongated fissure extending from the jugular foramen to a 

 small bridge of cartilage which cuts off the capsulo occipital 

 fissure, and it is believed that this long cleft represents the metotic 

 fissure of the lower forms. Upon examining the illustration 

 of Levi's 17 mm. stage it is found that the aforementioned small 

 bridge of cartilage has considerably widened ventro-medially, 

 and in the subsequent 28 mm. stage the squama and the pars 

 canalicularis are united as far as the jugular foramen. In both 

 the 17 and the 28 mm. stages of Levi the union was marked 

 by a separating sheet of perichondrium. 



At the caudo-ventral extremity of this union there is seen a 

 small notch, passing laterally from the outer part of the jugular 

 foramen to lose itself upon the external surface of the skull, just 

 above and behind the tip of the paracondyloid process. 



It may be noted that the otic capsule, between its dorso-lateral 

 connection with the squama and its ventro-medial connection 

 with the planum basale, forms a bridge, uniting these structures, 

 roofing the recessus supraalaris, and affording an upper delimita- 

 tion for the foramen jugulare. 



Dorsal to the capsulooccipital fissure the upper border of the 

 squama proceeds backwards and inwards, and describes a curve 

 with concavity upwards, to reach a small eminence, seen in the 

 Hertwig and other models, which may be known as the dorsal 

 occipital prominence (figs. 1 and 2). Beyond this it falls away to 

 join with the upper border of its partner of the opposite side, 

 this junction resulting in the formation of a dorsal concavity, 

 directed upwards, which marks the upper edge of the tectum. 

 Between the capsulooccipital fissure and the dorsal occipital 

 prominence the squama is continuous cranially with the parietal 

 plate. The line of union of the two lies at the bottom of a groove, 

 seen from the inner aspect of the skull. It may be known as the 

 occipitoparietal groove (fig. 1) and presents, on the right side two 

 perforations, on the left one, through which small veins pass. 

 The paired foramen (known as the occipitoparietal fissure, (figs. 

 3 and 5), is the larger, is elongated, and is situated about 

 midway between the extremities of the groove. It perforates 

 the groove at the most caudal part of its course. The smaller 



