rilE ANATOMY OF BllWti.— 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 otli(;r water birds; tit;, (i'i, «c), for lodgment oi tlie 

 sujira-orbital gland, the secretion of whieli lubricates tlu' nasal [lassages. 'J'hi; cerebral plate (jt 

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

 for the exit of nerves which are always foun<l at the back of tlie orbit. View from above, the 

 frontal is vaulted and c.Kpauded behind, over the l)rain cavity, then pinched more or less, s(jme- 

 times e.Ktremely 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 lacrynial reginn, 

 is very great in the duck I'amily, as seem in hg. (>.'!. 



The Squamosal (Lat. squama, a scab' ; tigs. 70, 71, .s'^.) liounds the brain-box laterally, 

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

 obliterated in adult life. It is situated near the h)wer back lateral corner of the skull, foiiiiing 

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

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

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

 « ard spur, the squamosal process (fig. 62), looking like a duplicate post-frontal ])rocess ; 

 between these two is the crotaphijte depression, corresjxinding to tlie "temporal fossa" of man, 

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

 adjacent part of the orbit being alisphenuidab 



The Periotie Bones (Gr. irepl, peri, about; our, cii-df, ous, olos, the ear; fig. 7')) are 

 those that form the jjeirosal bone (Lat. petrostis, rocky, from their hardness), or bony periotie 

 capsule, containing the essential organ of hearing. Wlien united witli each other and witli tli(! 

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

 omy. There are tliiee of these otic bones, — an anterior, the pro-otic; a ]iosterior and inferior, 

 the opisthotic (Or. oina-df, opisthe, behind) and a superii.ir and external, the epiotic. 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 tlie opisthotic, whicli there fuses indistiuguisliably 

 with the exoccipital. But somewhat of these bones arc s(.'en on looking into the cavity of tlie 

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

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

 The cavity of the periotie bone is hollowed 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 skull vievi'ed 

 internally (fig. 70), Parker figures a very large jjrootic portion {po) of the jieriotic, perforated 

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

 and behind the prootic a small opisthotic (op), in ndation with the exoccipital, upon tin; surface 

 of which it also appears, outside (fig. 69, at /;sc), and with whicli it blends; a very small epiotic 

 centre {ep), between the prootic and snpraoccipital ; and the anterior semicircular canal {asc) 

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

 matically. According to Huxley's generalization, the epiotic is in special relation with tin! 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 <|uadrate is implanted is prootic. Below the drooping eaves of the squamosal, 

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

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



fore pviiperly a, pnst-frontal, bone. Or, again, that U. may Iiavc nntliing to ilo witli tlie froiifal bone, but belong to 

 tlie alisplienoid, as a jirocess of tlie latter or a separate ossiflcalion ; in wbieli case it would bo properly tlie sphe- 

 nottc. In no event lias it anything to do with the squamosal process lettered as such in fig. G'2. 



