215 



1111. The proximal phalanx of the principal digit, answering to the third or ' me- 



dins ' of tin- same pinion. 



The pneumatic foramina are numerous, and occasion a reticulate structure at the exterior 

 part of the bone. 



Ihntrrum, 



1112. The sternum of a Wild Swan (Cyy*** Bcmctii). 



The keel is excavated, not onlj for the reception of an air-cell, but likewise for a fold of 

 the wind-pipe, which fold expands with age and lies horizontally in the substance of the back 

 part of the sternum : small pneumatic foramina are situated at the anterior and inner surface 

 of the bone, and perforate the articular surface* for the sternal ribs. 



IluHteria*. 



1113. A longitudinal section of a tibia of an Ostrich (Stntkio Camehu). 



The walk of the shaft are dense and thick, and lined by a layer of looser oanccllous tex- 

 ture, which forms the greater part of the substance of the two extremities. No air prnr- 

 Uratea this bone. The medullary rarity is large, and much of its surface is smooth : the 

 arteria medullaris perforates the bone near the termination of the fibular ridge ; the canal 

 extend* obliquely downwards, divides, and its two inner orifices may be seen below the middle 

 of the shaft. 



1114. A longitudinal section of the tarso-mctatarsal tx>nc of the same Ostrich (Mm- 

 Mo Camehu). 



A larger proportion of its proximal extremity is occupied by a rancelluus texture, closer 

 than that of the pneumatic bones. The compact walls of the shaft are as thick as usual in 

 the marrow-bones of birds of this site. The inner surface of the medullary cavity is smooth. 

 The exterior short process above the distal condyle indicates the termination of the abortive 

 digit. The large canal perforating the proximal end of the bone from before backwards 

 indicates the primitive division of the two normally developed but now coalesced metatanals. 



1115. The metatarsus of a young Ostrich (Slrutkio Camtiiu). 



The single booe, or epiphysis, representing, in part, the tarsus, has been removed from the 

 of the three metatanals, which coalesce with it, and with each other, to form the 

 ; segment of the leg. The primitive clefts still extend some way down and may be 

 traced to the distal end : the metatarsal which rapports the largest claw has the cmallest 

 proximal end, that which supports no claw has the largest. 



Pretexted by Prof Ovn, F.R.S. 



