1888.] On Structures found in the Skull of Birds. 



397 



selves respectively dorsad and ventrad, forming two horizontal scrolls, 

 which become simpler and simpler, finally being reduced to a single 

 narrow horizontal plate, which is continued as far forwards as a small 

 arterial foramen in the lateral ethmoidal cartilage at the junction of 

 its 3rd and 4th portions. 



In addition to these, which may be called the turbinals proper, the 

 5th anterior (free) portion of the lateral ethmoidal cartilage sends 

 inwards for a short . distance a narrow horizontal shelf-like process 

 (fig. 3, sect. 5), beginning immediately caudad of the nostril, and 

 nearly as far back as the junction of the lateral ethmoids with the 

 mesethmoid. 



On each side of the ventral edge of the mesethmoid, in the vomerine 

 region is a slender, free rod of cartilage, shaded dark in fig. 2, imbedded 

 in connective tissue, and lying parallel with, and either immediately 

 above or slightly laterad of, the dorsal edge of the vomer. It is abotit 

 10 mm. long, and about 0\L4 mm. in diameter. This is obviously 

 the vestio-ial cartilage of Jacobson's organ, figured but not described 

 in " Ostrich Skull " (Plate 10, fig. 14), described in " Skull of Bird," 

 Plate 2 (p. 109, Note) : called upper labial in Snake (Plate 30, fig. 2j, 

 and nasal floor in Lizard (Plate 44, figs. 3 and 4). 



III. u On Remnants or Vestiges of Amphibian and Reptilian 

 Structures found in the Skull of Birds, both Carinatse and 

 Ratitae." By Wl E. Parker, F.R.S. Received February 9, 

 1888. 



One of the most remarkable structures found in the skull of cer- 

 tain Amniota or higher Yertebrata— Reptiles and Mammals, is the 

 so-called "Jacobson's organ." 



A pair of these carious gland-like bodies, each carefully placed in 

 its own special capsule, may be seen in Serpents, Lizards, and 

 Mammals ; but they are not present in Tortoises, Crocodiles or Birds, 

 as far as our present knowledge goes. Rathke, in his work on the 

 Snake's Skull, spoke of the "nasal glands and their capsules," and 

 for a long while this term made them to be confused with the nasal 

 glands of birds, which have nothing whatever to do with " Jacobson's 

 organs." 



These structures are largest in Serpents, Lizards, and Monotremes, 

 next in order come the Marsupials, Edentates, and Insectivores, then 

 the Mammalia generally, including Man himself, in whom they appeal' 

 for a time, and then vanish away* 



These structures lie just above the anterior incisive foramina. I 



* See Kolliker, ' TJeber die Jacob son' schen Organe des Menschen,' Leipzig, 

 1877. . . 



