280 



AVES. 



from below upwards and forwards ; it is sepa- 

 rated from the upper and lateral regions by a 

 well developed, sharp, lam bdoidal crest; and it 

 is divided into two lateral moieties by a slight 

 longitudinal ridge. The temporal fossae are 

 deeper and wider than in any of the preceding 

 orders; and they now extend upwards, as in 

 many of the carnivorous mammalia, to the sa- 

 gittal line, along which an osseous crest is 

 developed to extend the surface of attachment 

 of the temporal muscles. The cranium is ex- 

 panded, anteriorly to the above fossae, as if to 

 allow of a compensating space for the develop- 

 ment of the cerebral hemispheres, the interspace 

 of which is indicated by a deep longitudinal 

 furrow, almost peculiar to these genera of 

 birds. The roof of the orbits is expanded late- 

 rally, which gives great breadth to this part of 

 the head, but the posterior orbital walls are 

 very imperfect, and the internal walls or septum 

 almost wholly wanting. The optic foramina 

 are blended with each other and with the 

 smaller foramina, which in other birds represent 

 the foramen lacerum orbitale. The anterior 

 boundary of the orbits is also very imperfectly 

 completed, the ungueo-naso-maxillary and an- 

 terior nasal fissures are not remarkable for their 

 extent. 



Woodcocks, Snipes, Curlews, and Lapwings, 

 resemble Herons in their defective bony orbits ; 

 but they want the extended superior parietes 

 of those cavities, and differ much in the al- 

 most spherical form of the cranium, which is 

 smooth and devoid of the muscular ridges 

 characteristic of the fish-feeding Gralla. In 

 this order the intermaxillary bones present 

 some of their most eccentric forms. They are 

 narrow, elongated, and curved downwards in 

 the Ibises and Curlews ; bent upwards in the 

 contrary direction in the Avosets; extended in a 

 straight line in the Snipes ; singularly widened, 

 and hollowed out in the Boat-bill ( Cancroma); 

 widened, flattened, and dilated at the ex- 

 tremity in the Spoon-bill ; thickened, rounded, 

 and bent downwards at an obtuse angle in the 

 Flamingo. 



Among the Natatores, the sea-birds, as 

 the Divers, (Colymbus), Grebes, (Podiceps), 

 and Cormorants (Carbo), are characterized 

 for the defective condition of the bony orbits, 

 and of the anterior parietes of the cranium ; 

 the septum of the orbits is almost entirely 

 wanting; in place of the posterior parietes 

 there are two lacunae leading directly into the 

 cranial cavity, one superior, of large size, 

 and one inferior, smaller ; they are, in 

 general, separated by a narrow osseous bar, 

 but in the Coulterneb, (Fraterculu arctica) 

 this is also wanting, so that all the anterior 

 cerebral nerves escape by a common open- 

 ing. But in this species it must be observed, 

 that the vertical lamina of the sethmoid is 

 ossified at its posterior part. In the Petrels 

 and Albatrosses, the internal and posterior 

 walls of the orbits are more complete. In 

 the Diomedea exulans the optic foramina are 

 separated both from each other, and from 

 the neighbouring outlet. The occipital re- 

 gion is low, and divided into a superior and an 



inferior facet, the latter being concave from side 

 to side. The plane of the occipital foramen is 

 almost vertical. The occipital or latnbdoidal 

 crista is well-marked, and the temporal fossae 

 nearly approximate in the middle line. In 

 these sea-birds and in the Gulls, the lateral 

 lacunae in the bony parietes of the face are 

 very considerable. 



A most remarkable characteristic of the cra- 

 nium of both the Brachypterous and Macro- 

 pterous Sea-birds is the presence of the two 

 deep, elongated, semilunar gland ulardepressions 

 before mentioned, extending along the roof the 

 orbits. In the'aquatic birds which frequent the 

 marshes and fresh waters, as the Anatida or 

 Lamellirostres, these glandular pits are want- 

 ing, or very feebly marked, as in the Swans. 

 They are, however, again met with of large 

 size, though shallow, in the Curlews (Nume- 

 nius) and Avosets (Recurvirostra); and are 

 also found, though of smaller size, in the 

 Flamingo. 



Of the thorax. In every part of the skele- 

 ton of Birds, we may observe that there is 

 a close adherence to the oviparous modification 

 of the vertebrate type of structure. This is 

 manifested in the forms and connections of the 

 several vertebrae, and of the cranial bones. 

 It is no less conspicuous in the structure of 

 the thorax. 



The ribs are apparently in moderate num- 

 ber, but when their analogues are closely 

 sought for, they are found to extend, as in 

 the Crocodile, along the greater part of the 

 cervical region. In fact the small styliform 

 processes which point backwards from the 

 lateral projections on the anterior parts of the 

 bodies of these vertebras remain separate after 

 the true elements of the vertebrae have coalesced. 

 In an Ostrich which had attained half its groxvth, 

 we have found these spurious ribs still moveable. 

 They anchylose, however, with >the transverse 

 processes in general long before the growth of 

 the individual is completed, excepting towards 

 the caudal extremity of the cervical region, 

 where comparative anatomists, from this cir- 

 cumstance, have always found a difficulty in 

 determining the commencement of the dorsal 

 vertebrae. If the moveable ribs had com- 

 menced, as in Mammalia, by extending to the 

 sternum, the determination of their number 

 would have been easy; but they begin, some- 

 times by a gradual and at others by a sudden 

 elongation,* opposite the furculum, from which 

 point, either one, or two, as in the Humming- 

 bird, (see p, Jig. 125,) terminate by extremities 

 imbedded in muscle, and unconnected with 

 any corresponding portion extending from the 

 sternum. 



Meckel considers the true number of ribs 

 in the Diurnal Raptores to be nine pairs, 

 of the Nocturnal eight; in the Insessores seven 

 or eight; in the Scansores nine, except the 

 Cuckoo, which has seven or eight ; in the 



* This is remarkably the case in the Wood- 

 Grouse ( Tetrao Urogallus), where the penultimate 

 and last cervical ribs, instead of gradually enlarg- 

 ing, diminish in size, so that the determination of 

 the first thoracic rib is easy. 



