188 APPLICATION OF PHOTOGENIC DRAWING 



auditory bulla, and joins a similar band which forms part of 

 the supra-occipital bone. In the genus Alactaga the audito- 

 ry bullae are comparatively small, and the peculiar bands just 

 described do not appear to exist. 



In the form of the lower jaw the genus Dipus very closely 

 resembles Myoxus, especially My. avellanarius ; in both the 

 descending ramus is perforated, and in Myoxus as in Dipus 

 the glenoid cavity of the temporal bone is oblique, though in 

 a less marked degree. On the other hand we find a conside- 

 rable resemblance, in the palate and its foramina, between 

 the animals of the present family and those of the genus Ger- 

 billus. 



The genera Dipus, Alactaga, and Meriones belong to the 

 present family ; I must observe however that the Dipus Ca- 

 nadensis, (which constitutes the genus Meriones, according 

 to most of the later writers), presents a form of skull which, 

 in many respects, is intermediate between the jerboas and 

 the dormice {Myoxidce). Comparing the lower jaw of Dipus 

 JEgyptius with that of Myoxus avellanarius, we perceive 

 that the coronoid process is proportionately larger in the lat- 

 ter ; in this respect the Meriones Canadensis agrees with the 

 dormouse ; it also approaches more nearly to the last-men- 

 tioned animal in the comparatively small extent of the pala- 

 tine portion of the palate bone. In the size of the ant-orbital 

 foramen, the Mer. Canadensis is intermediate between the 

 two animals with which we are comparing it. This foramen 

 being larger than in Myoxus, and smaller than in Dipus. In 

 Mer. Canadensis, as in the jerboas, the portion of the zygo- 

 matic process of the maxilla which forms the lower boundary 

 of the ant-orbital passage is thrown out from the plane of the 

 palate. The incisive foramina are larger in Mer. Canaden- 

 sis than in Myoxus avellanarius, thus agreeing with Dipus. 



(To be continued.) 



Art. X. — Observations on the application of Heliographic or Pho- 

 togenic Drawing to Botanical Purposes ; with an account of an 

 economic mode of preparing the Paper : in a Letter to the Editor 

 of the * Magazine of Natural History.' By Golding Bird, 

 M.D., F.L.S., &c. 



Sir, 



The mode of fixing the images of the camera 

 obscura, and copying engravings, by means of the chemical 

 action of light on paper prepared with a solution of chloride of 



