ENCEPHALOCELES AND OTHER ABNORMALITIES. 95 



SKELETON. 



A dissection of the skeleton was made, the vertebrae and ribs being left con- 

 nected by their ligaments, so that the specimen could be easily mounted. To 

 facilitate handling, two transverse cuts in the skeleton were made at the level of 

 the first thoracic and first lumbar vertebrae. A study of the skeleton shows marked 

 maldevelopment and distortion, as may be seen in figures 10, 11, and 12. The 

 axial skeleton is most affected, the arches of all the vertebrae being defective; these 

 are open posteriorly in the midline and are flattened outward, forming wide anterior 

 support for the central nervous system. In the cervical and thoracic regions the 

 bodies of the vertebras are fused, shortened, and dorsally flexed, so that the spine 

 is bent almost double. The occiput actually rests on the gaping vertebral arches 

 and fuses with them. 



Viewing the occiput in figures 13 and 14, the inferior and medial two-thirds of 

 the squama occipitalis is seen to be defective. A bilateral bony excrescence on 

 its dorsal surface, near the defective medial margin of the squama and close to its 

 junction with the partes laterales joins it to the everted arches of the second lumbar 

 vertebra on the left side and to the first lumbar vertebra on the right. The defect 

 of the squama in the midline, together with a widening of the angles formed by the 

 junction of the pars basalis with the partes laterales, has greatly increased the size 

 of the foramen magnum. This is oval in shape and measures 4.5 by 3.7 cm. The 

 long diameter is antero-posterior, and posteriorly it slants slightly to the left. 

 For purposes of comparison the size of a normal foramen is indicated in figure 13 

 by means of dotted lines. The large foramen resembles that of the chondro- 

 cranium at a very early stage of development. The participation of both the squama 

 occipitalis and the vertebral arches in the midline defect, as it exists here, has been 

 regarded as teratological evidence of the homology of these parts, and probably 

 has been a factor in advancing the opinion, which has slowly gained ground, that- 

 some cranial defects, even when existing alone, belong in the same category with 

 certain vertebral abnormalities. 



The two partes laterales are well formed and but slightly asymmetrical. The 

 left jugular process is more marked than the right. On the left inferior surface 

 directly under the jugular process there is a cartilaginous prominence which meets 

 the tip of the transverse process of the underlying atlas. The hypoglossal foramen 

 on the left side is a single canal, and while the right hypoglossal foramen has a single 

 perforation on the medial surface of the pars lateralis, it has a double exit on the 

 outer surface of the bone. A small rod of bone divides it into a smaller anterior 

 and a larger posterior foramen, as is demonstrated in figure 11. A division similar 

 to this has been observed frequently in embryological studies and appears on the 

 left side in a skull of a human fetus modeled by Macklin. The condition is of rather 

 frequent occurrence. Lillie gives a ratio of 14 per cent complete division and 

 36 per cent indicated division, out of 305 left and right canals examined by him. 

 The explanation generally offered is that it is persisting tissue from primitive 

 cranial divisions which usually disappear at a very early stage. 



