120 BULLETIN UNITED STATES GEOLOGICAL SURVEY. Wol.Yl. 



marks, allow it to rest liexe and i^roceed with the true object of this 

 paper, a description of its skeleton, simply reminding the student that 

 of all the several genera that go to make up the family Alaudidcc, or 

 Larks, but one genus has fallen to the lot of the North American fauna, 

 and that the genus contains but one species, with its varieties, the oste- 

 ology of that species being the subject of the present article. 



The sliull— (PL IV, Figs. 22, 25, and 26).— It is a striking characteristic 

 in the skulls of nearly all adult birds that certain bones become firmly 

 united, their sutures entirely disappearing; perhaps in no species of the 

 highly organized suborder Oscines has this almost universal avian feature 

 been so thoroughly carried out as in our present subject, the Horned 

 Lark. Occasionally we do find, however, a trace to guide us in locating 

 the original boundaries of the primitive elements, even among the Os- 

 cines, as the sutures, amidst the i)arietals and frontals in the cranium of 

 Lanhis, when maceration is carried to a high degree, but in Eremopliila, 

 as already stated, there is a total absence of any such indication. If we 

 remove the lower mandible from the skull in any of the class Aves, and 

 place the remainder on the horizontal phxne, with the basi-cranii down- 

 wards, we observe that in difl'erent skulls there exists in this position 

 differences in equilibrium, and differences in, what we will caU, the an- 

 terior and posterior hearing points, or the points upon which this part 

 skull we are studying, we find, when it is placed as directed above, 

 of the skull rests on the horizontal plane. To illustrate this in the 

 that its equilibrium is quite stable, and that it rests posteriorly upon 

 the tympanies, anteriorly upon the tip of the superior mandible, which 

 constitute, respectively, its posterior and anterior bearing points. In 

 this case there is but one anterior bearing point, with two posterior 

 ones. This is a very common result, but there are at the same time 

 many exceptions to it, as in Numenius and many species of the family 

 Anaiidce. 



Again, if we erect a perpendicular from one of the posterior bearing 

 l^oints, or the posterior bearing point, for sometimes it is the condyle, 

 we find that the planes passing through the circumference of the fora- 

 men magnum and the occipital vertebra, and the point where the foot 

 of this perpendicular and the posterior bearing points coincide, make 

 certain angles with the horizontal plane (the ordinary horn protractor 

 is the best instrument to take these angles with), which we will call, re- 

 si3ectively, the angle of the foramen and the angle of the base. These two 

 angles, in many instances, practically coincide, as in our Lark, where 

 they make an angle of 40c> with the horizontal plane. In the cut, H H' 

 is the horizontal i^lane ; a the anterior and 2J the posterior bearing points. 



These angles also differ in many birds ; e. g. , the anterior bearing 

 point in Ardea herodias is the tip of the upper mandible, the posterior 

 ones being the inner of the three facets on each tympanic ; the angles 

 of the planes of the base and foramen about coincide, and is 50°. In 

 many of the Owls and diurnal birds of prey, the bearing points being 



