THE ANATOMY OF BIBBS.— OSTEOLOGY. 157 



it is usually quite prominent. The frontal rim of the orbit in many birds shows a crescentic 

 depression (very strong in a loon and many other water birds; fig. 63, w), for lodgment of the 

 supra-orbital gland, the secretion of which lubricates the nasal passages. The cerebral plate of 

 the frontal is often imperfectly ossified, showing large " windows" besides the regular openings 

 for the exit of nerves which are always found at the back of the orbit. View from above, the 

 frontal is vaulted and expanded behind, over the brain cavity, then pinched more or less, some- 

 times extremely narrow over the orbits, then usually somewhat expanded again at the fronto- 

 facial suture. The extent of the.frontal between the orbits and face, in the lacrymal region, 

 is very great in the duck family, as seen in fig. 63. 



The Squamosal (Lat. squama, a scale ; figs. 70, 71, sg.) bounds the brain-box laterally, 

 between occipital, parietal, frontal and sphenoidal bones, its distinction from all of these being 

 obliterated in adult life. It is situated near the lower back lateral corner of the skuU, forming 

 some part of the cranial wall just over the ear-opening, and a strong eaves for that orifice. It 

 is firmly united also to the bones of the ear proper, and receives the larger share of the free 

 articulation which the quadrate has with the skull. It often develops a strong forward-down- 

 ward spur, the squaiAosal process (fig. 62), looking like a duplicate post-frontal process ; 

 between these two is the crotaphyte depression, corresponding to the "temporal fossa" of man, 

 in which lie the muscles which close the jaws. It scarcely or not enters into the orbit, the 

 adjacent part of the orbit being alisphenoidal. 



The Perlotic Bones (Gr. nepi, peri, about ; ovs, wrdr, ous, otos, the ear ; fig. 70) are 

 those that form the petro^fil bone (Lat. petrosus, rocky, from their hardness), or bony periotic 

 capsule, containing the essential organ of hearing. When united with each other and with the 

 squamosal, they form the very composite and illogical bone called "temporal" in human anat- 

 omy. There are three of these otic bones, — an anterior, the pro-otic; a posterior and inferior, 

 the opisthotic (Gr. Sma-Be, opisthe, behind) and a superior and external, the epiotio. They can 

 only be studied in young skulls, upon careful dissection ; they do not appear upon the outside 

 of the skull at all, excepting a small piece of the opisthotic, which there fuses indistinguishably 

 with the exoccipital. But somewhat of these bones are seen on looking into the cavity of the 

 outer ear, and if the fenestra ovalis can be recognized, it determines a part of the boundary 

 between the prootic and opisthotic bones, while the fenestra rotunda lies wholly in the latter. 

 The cavity of the periotic bone is hoUowed for the labyrinth of the internal ear, including the 

 cochlea, which contains the essential nervous organs of hearing, and the three semicircular canals 

 — so much of them as does not invade surrounding bones. In the young fowl's skuU viewed 

 internally (fig. 70), Parker figures a very large prootic portion (^o) of the periotic, perforated 

 by the internal auditory meatus (7) for the entrance from the brain of the auditory nerve : below 

 and behind the prootic a small opisthotic (fip), iu relation with the exoccipital, upon the surface 

 of which it also appears, outside (fig. 69, at ^sc), and with which it blends; avery small epiotic 

 centre {ep), between the prootic and supraocoipital ; and the anterior semicircular canal (a«c) 

 embedded in the latter. In Dr. Shufeldt's figure the otic elements are merely noted diagram- 

 maticaUy. According to Huxley's generalization, the epiotic is in special relation vrith the pos- 

 terior semicircular canal ; the prootic with the anterior vertical canal, between which and the 

 foramen ovale (5) for the lower divisions of the trifacial nerve it lies. That part on which the 

 inner foot of the quadrate is implanted is prootic. Below the drooping eaves of the squamosal, 

 before the flaring vidng of the exoccipital, and behind the quadrate bone, is the always decided 

 and considerable cavity of the ear, bounded pretty sharply by the squamosal and exoccipital rim, 



fore properly a, post-frontal bone. Or, again, that it may have nothing to do with the frontal bone, but belong to 

 the alisphenoid, as a process of the latter or a separate ossification; in which case it would be properly the sphe- 

 notic. In no event has it anything to do with the squamosal process lettered as such in fig. 62. 



