605 



situated at the upper part of the head as to admit of the animars 

 breathing while only a small portion of its head is above the water. 

 In its descent through the skull, between the cranial and facial bones, 

 the tube is divided by a thin plate of bone into two nasal canals, 

 which form, below this partition, a single muscular tube opening at 

 its lower part into the pharynx by a constricted aperture, through 

 which the larynx projects upwards quite through the pharynx, di- 

 viding it into two channels. A series of pouches, five in number, 

 capable of great dilatation, and provided with a muscular apparatus 

 for retaining or expelling their contents, communicate by large ori- 

 fices with the nasal canals, and appear to correspond in situation 

 with the antra, frontal sinuses and ethmoid cells. The author gives 

 a minute anatomical description of these muscles, and an account of 

 their modes of action ; the adjustments of the apparatus being such 

 that the outer passage may be closed or opened above or below the 

 anterior pouches. When the outer passage is closed, the posterior 

 pouches can be distended and the anterior emptied ; while the con- 

 verse may be effected when the passage is open. The use of the 

 pouches appears to be to buoy up the head, so that on the porpoise 

 rising from deep water, the opening for breathing comes first to the 

 surface and admits of the animal's sleeping in that position, while its 

 whole body remains imraer.sed in the water. 



" On Motion in the Lumbar Division of the Spine in Birds." By 

 George Oakley Fleming, M.D., F.L.S. Communicated by Thomas 

 Bell, Esq., F.R.S. 



The author gives quotations from the M orks of Cuvier, Blumen- 

 bach, Tiedemann, Macartney, Vicq d'Azyr, Cams, Earle, and Roget, 

 in proof of its being the prevalent opinion among comparative phy- 

 siologists that the dorsal and lumbar portions of the spine form alto- 

 gether a rigid structure, not admitting of the least perceptible flexion. 

 But from his observations of the form of the articulating surfaces of 

 the lumbar vertebrae, which appear to be adapted to lateral motion, 

 the author was led to conclude that, although flexion in the mesial 

 plane is effectually prevented, some degree of lateral flexion actually 

 takes place. The number of articulations in this part of the spine, 

 he observes, varies in different birds : thus in the sea-gull, there are 

 several articulations in the dorsal and lumbar portions ; while, in the 

 peacock, there is only one move'able vertebra; the remaining dorsal 

 being united together, and all the lumbar vertebrae being consoli- 

 dated and anchylosed with the sacrum ; thus forming two firm and 

 immoveable pieces between which the moveable vertebra is placed. 

 The flexion of the spine forwards is prevented by the great breadth 

 of the spinous processes and their projections at right angles to the 

 bodies of the vertebrae ; and frequently also by the addition of a 

 number of thin, flat long bones which are applied by their flat sur- 

 faces on each side of the spinous processes ; and also by strong flat 

 ligaments, situated between each spinous process, like the ligamen- 

 tum nuchae of herbivorous quadrupeds. For the purpose of guard- 

 ing against pressure on the spinal cord during the lateral flexion of 



