232 GENERAL ORNITHOLOGY part ii 



which are always found at the back of the orbit. Viewed from above, 

 the frontal is vaulted and expanded behind, over the brain cavity, 

 then pinched more or less, sometimes extremely narrow over the 

 orbits, then usually somewhat expanded again at the frontofacial 

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

 the lacrymal region, is very great in the duck family, as see in Fig. 63. 



The Squamosal (Lat. squama, a scale ; Figs. 70, 71, sq) 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 skull, 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-downward spur, the squamosal process 

 (Fig. 62), looking like a duplicate postfrontal process; between 

 these two is the crotaphite depression, corresponding to the "tem- 

 poral 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 Periotie Bones (Gr. inpl, peri, about ; oh, wto's, ous, otos, 

 the ear ; Fig. 70) are those that form thepetrosal bone (Lai. petrosus, 

 rocky, from their hardness), or bony periotie 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 anatomy. There are three of these 

 otic bones, — an anterior, the pro'dtic ; a posterior and inferior, the 

 opisthotic (Gr. otricrdi, opisthe, behind) and a superior 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 the opisthotic, which there fuses indis- 

 tinguishably with the exoccipital. But some part of these bones 

 is seen on looking into the cavity of the outer ear, and if the 

 fenestra ovalis can be recognised, it determines a part of the bound- 

 ary between the prootic and opisthotic bones, while the 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 organ of hearing, and 

 the three semicircular canals — so much of them as does not invade 

 surrounding bones. In the young fowl's skull viewed internally (Fig. 

 70), Parker figures a very large prootic portion (po) of the periotie, 

 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 (op), in relation with the exoccipital, upon the 

 surface of which it also appears, outside (Fig. 69, aApsc), and with 



