CHONDROCRANIUM OF A 20 MM. HUMAN EMBRYO 609 



at one point shows a prominence, the anlage of the pharyngeal 

 tubercle of the adult (fig. 3, 28) . 



The cranial area of the basioccipital is horizontal, thus making 

 the angle with the more caudal part, which has been already 

 mentioned in the description of the basal plate. It shows a 

 slight concavity from side to side on the dorsal surface, and a 

 corresponding convexity of the ventral. It gives origin on 

 either side to the cranial root of the occipital wing (fig. 1). 



The lateral parts of the occipital region may be said to take 

 origin by two roots with the hypoglossal canal between them. 

 The cranial entrance of this canal is divided on the left side by a 

 thin bar of cartilage (fig. 1, 35). This occupies only about one- 

 third of the length of the canal, which thus appears double re- 

 garded from the ental end, but single from the ectal aspect. 

 The two roots join lateral to the canal where they form a narrow 

 flat plate of cartilage with surfaces facing laterad and mesiad. 

 This plate widens quickly into the occipital wing and joins dor- 

 sally a thin plate of cartilage which surmounts the otic capsule 

 known as the parietal plate (figs. 1 and 2). 



After its junction with the occipital wing, the parietal plate 

 narrows to a thin ribbon of cartilage which turns mesially to 

 meet the corresponding process from the opposite side to form 

 the tectum posterius (fig. 1, -/). The central and lateral parts 

 of the occipital region, in conjunction with the tectum, thus 

 enclose the primitive foramen magnum. 



The occipital wing at its origin has two borders, cranial and 

 caudal (fig. 2). The cranial border bounds at first the jugular 

 foramen. It is a sharp ridge and shows at one point a protuber- 

 ance which Macklin takes to be the jugular tubercle of the adult. 

 Caudal to the jugular foramen the cranial border forms the inner 

 boundary of a space lying between the otic capsule and a lateral 

 extension of the occipital wing known as the lamina alaris. The 

 space is the jugular recess and in the adult condition, contains a 

 portion of the lateral sinus (fig. 7, 3). 



The caudal border of the occipital wing bounds the foramen 

 magnum (fig. 3). It passes from the condyle, the ventral fora- 

 minal prominence of Macklin, making a concave edge to the 



