12 



carpentry, they are produced by difFereut processes in the Mammal 

 and the Reptile. The zygapophyses exist in both ; to these, in the 

 Mammal, are superadded the joints developed on metapophyses and 

 anapophyses, which are below the zygapophyses ; but in the Serpents, 

 the superadded joints are on parts ^yhich the author terms the ' zygo- 

 sphene' and ' zygantrum,' and are above the zygapophyses. Some 

 characteristic differences are next pointed out in the Ophidian ge- 

 nera Coluber, Hydnis, Naja, Crotalus, Python, and the extinct 

 genus of large serpents from British eocene strata cdi\\e(\. PalcEophis, 

 The author also points out that the tenon -and-mortice joints are not, 

 as was supposed, peculiar to the Ophidian reptiles, but exist in the 

 Iguana, where they are likewise due to the superaddition of zygo- 

 sphenal and zygantral articulations. 



The author finally enters upon the comparative anatomy of the 

 ' hypapophysis,' that name being applied to the process, commonly 

 exogenous, from the under or ventral surface of the centrum, rarely 

 autogenous from the same aspect of the capsule of the notochord. 

 The modifications of the hypapophysis are exemplified in the Hare 

 and Rabbit, the Cape Jerboa, the Hydromys, the PJwca grcenlandica 

 and Lej^tonyx serridens, in the Hippopotamus, the Megaceros, the 

 Musk-deer, the Camel, the Giraffe, and other Ruminants. In the 

 OrnithorJiynclius the atlas is remarkable for a pair of hypapophyses, 

 like the first vertebra in the Sudis or Arapaima gigas : but the most 

 remarkable instances of the development and modification of the 

 hypapophysis are to be met with in the class of Birds. It is there 

 well-marked in the anterior cervical vertebrae, especially in the den- 

 tata, and reappears in the lower cervicals as a pair of processes, which 

 defend and sometimes encompass the carotid arteries, forming a 

 quasi-haemal arch, as in the Pelican. The still more extraordinary 

 developments of the hypapophysis in the Aptenodytes and SphcBnis- 

 cus are specially described and illustrated by figures. The modifi- 

 cations of the same process are pointed out in some extinct Reptilia, 

 as e.g. the Crocodilus basijissus, the Mososaurus, the Iguanodon and 

 the Ichthyosaurus : in the latter the hypapophysis is exogenous in 

 the neck, as in some Lizards, and forms the so-called ' wedge-bones 

 the part usually called ' body of the atlas ' is serially homologous 

 with these ; the true centrum of that vertebra being the so-called 

 odontoid process. The memoir concludes with a demonstration of 

 the serial homology of the haemal arches of the tail, sometimes called 

 chevron-bones, and the essential distinction of the hypapophyses from 

 the h^mapophyses, and at the same time from the parapophyses, with 

 which the hypapophyses co-exist in the cervical and anterior thoracic 

 regions of the Crocodile. 



The paper is illustrated with fifty-five drawings, of which detailed 

 descriptions are appended to the memoir. 



A communication was read, entitled, " Researches on the Distri- 

 bution of Vegetables in the Alps compared with the Differences of 

 Climate, and on the Periodical Development of Plants at different 

 heights." By Adolph Schlagintweit. 



