MUSEUM OF COMPARATIVE ZOOLOGY. 223 



Fig. 3. A sketch of the left half of the hemisected cranium of Chlamydoselachus 

 to show the relations of the notochord and cranial aorta to the basis cranii and to 

 the pituitary prominence and space. Natural size. 



Fig. 4. (a) A view of the inner surface of floor of the cerebral cavity in the 

 pituitary region before the removal of the dura mater and tissue which separates 

 the brain cavity from the pituitary excavation and its contents (pituitary plexus, 

 transverse canal, and carotid chiasm). Natural size, (o) A dissection of the 

 ventral surface of the same, to show the chiasm of the internal carotids. 



Fig. 5. A series of seven transections of the basis cranii to show the relations 

 of the notochord, cranial aorta, and the median ventral groove to each other and 

 to the cranial floor. 



Figs. 5 a and 5 6 from 1 shown in Fig. 1. Figs. 5 c and 5 c? from 2; Fig. 5e 

 from 3; Figs. 5/ and 5a from the pituitary prominence. All the figures enlarged. 

 The series progresses cephalad, and the geometrical outlines refer to portions of 

 the median line of Fig. 1. 



Fig. 6. Part of the section of the notochord figured in 5 a more highly magni- 

 fied to show the sheaths and external calcified layer. X circa 180 diameters. 



Fig. 7. A section of the cranial aorta from Fig. 5 d, more highly magnified. 

 The fibrous trabeculae cross the cavity of the vessel in all directions. X 180 

 diameters. 



Fig. 8. A transsection of the basis cranii of Chlamydoselachus, near the verte- 

 bral articulation, to show the figure made by the calcareous sheath (and its pro- 

 cesses) of the notochord, resembling a vertebra of the trunk region. 



Fig. 9. A transversely cut piece from the basis cranii of Heptabranchias sp. 

 near the anterior third of the distance between the pituitary prominence and the 

 occipital region, to show the chorda (and aorta ?) and the blood-vessels enclosed in 

 the cartilage. 



Fig. 10. The efferent branchial system and aorta of Zygcena malleus, after Hyrtl. 



Fig. 11. Diagram of the above, with the " cranial aorta" inserted. 



Fig. 12. The efferent branchial system of Mustelus antarcticus, after Parker. 



Fig. 13. The efferent branchial system of Myxine, after Miiller. 



Fig. 14. The cephalic circle of Cephaloptera modified after De Sanctis. 



