. The elasmobranch fishes. Chondrichthyes. 274 THE ELASMOBRANCH FISHES DEVELOPMENT OF EAR The ear {Scyllium, fig. 239), like the nose, forms as a pit. In the development of the ear, however, the vesicle thus formed sinks in and, as the sacculus (s.), becomes far removed from the exterior. It does not, however, lose entire con- nection with the outside for as it sinks inward it becomes flask-shaped, the long neck being the endolymphatic duct {). At this stage the outer wall of the vesicle becomes thin and the anterior oblique and horizontal semicircular canals {aos. and hr.) de- velop from
. The elasmobranch fishes. Chondrichthyes. 274 THE ELASMOBRANCH FISHES DEVELOPMENT OF EAR The ear {Scyllium, fig. 239), like the nose, forms as a pit. In the development of the ear, however, the vesicle thus formed sinks in and, as the sacculus (s.), becomes far removed from the exterior. It does not, however, lose entire con- nection with the outside for as it sinks inward it becomes flask-shaped, the long neck being the endolymphatic duct {). At this stage the outer wall of the vesicle becomes thin and the anterior oblique and horizontal semicircular canals {aos. and hr.) de- velop from them. Sensory Canal System and Ampullary and Pit Organs The sensory canal system as we have seen in Heptanchus consists of exten- sive sensory canals over the head and along the side of the body. The am- pullary organs associated with cer- tain of the canals and innervated by the same nerves are confined to the region of the head. Certain modifica- tions of the latter, the vesicles of Savi, may also be present. The pit organs are mainly in the anterodorsal trunk region but some of them are in the segment of the head. Sensory Canal System The sensory canals take a general course parallel to the long axis of the body. In the region of the trunk and tail thej^ compose the lateral line ob- served in our study of external form, and in the region of the head they form the cephalic canals, three or four main divisions of which are present in the sharks. One of these, the supra- orbital canal {soc, figs. 240-242), runs above the eye; another, the infraorbital (ioc), passes back of and forward below the eye; the third or hyomandibular. Fig. 240. Dorsal view of cephalic canals in Laemargus. (From Ewart.) (Drawn as transparent object.) cc, commissural or supratemporal canal; lime, hyomandibular canal; ioc, infraorbi- tal canal; ZL,lateral canal; soc, supraorbital Please note that these images are extracted from scanned page images that may have been digitally enhanced for readabil
Size: 1067px × 2341px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublisherberkeleycalifuniversityofcaliforn
