1907. J Dr. Hossack . The Rats of Calcutta. 45 



Skull measurements. — This subject caused me some difficulty, and as I am uncer- 

 tain that my measurements were taken in the standard fashion, it seems best to give 

 a brief description of my methods. 



1. Greatest length =G.Iv — Taken with sliding callipers. The anterior point is 

 very variable, being the tip of the nasals in Mus decumanus, and the front of the 

 incisors in short-nosed N. bengalensis. The latter point of measurement is almost iden- 

 tical with what would be the most desirable one, namely, the most projecting point of 

 the premaxilla. The posterior point is equally variable, being sometimes the supra- 

 occipital ridge, sometimes the inion, sometimes the opisthion, sometimes the condyles. 



2. Basilar length to henselion = Basil. ly. — Taken with curved, fine-pointed 

 callipers reversed, from the pit behind the two incisors to the basion or anterior border 

 of the occipital foramen. This is unsatisfactory owing to the penetration of the callipers 

 into the pit depending on the closeness with which the incisors are approximated. The 

 callipers have to be excessively fine to get properly home in small M. rattus skulls. 



3. Greatest breadth = G.B. — From zygoma to zygoma, with sliding callipers. 



4. Nasal length =N.Iv. — From extreme point to extreme point, avoiding the 

 central notch where it is present. 



5. Interorbital breadth =Io.B. — The point of minimum breadth between the 

 orbits. The minimum point is a little below the edge of the orbit so that the callipers 

 have to be slightly opened in order to pass over the edges of the orbits. It is difficult 

 to take very accurately unless care is taken to slide the callipers off at the point where 

 the orbital edges are most close together. 



6. Cranial breadth = Cr.B. — Taken with callipers at the point of maximum breadth, 

 i.e., from a little pit just above the centre of the posterior root of the zygoma. In 

 M. rattus the maximum is found a little posterior to this pit. 



7. Length of zygomatic plate =Zy. PI. — Taken with callipers antero-posteriorly 

 from the deepest part of the posterior concavity to the most projecting point of the 

 anterior convexity. 



8. Palate length from henselion = Pal. L. — As in basilar length. 



9. Diastema, with callipers from most anterior point of edge of socket of first 

 molar to most posterior point of socket of incisor. 



10. Palatine foramina, length = Pal. For. L. — The anterior palatine foramina 

 are sometimes longer on one side than the other ; if so, take the mean of the two. 

 Whereas in the case of Nesokia the foramen narrows to a slit posteriorly, it may be 

 difficult to define that end of the foramen. 



11. Palatine foramina, breadth = Pal. For. B. — This is the width of the two 

 foramina combined. This measurement is very difficult to get accurately where the 

 foramina are very narrow, as the side walls of the foramen converge making an 

 edge-to-edge measurement much too large. In such cases I get the point of the dividers 

 inside the walls of the foramen and adjust them as accurately as possible to the max- 

 imum width of the black opening seen. 



12. Length of upper molar series = Up. Mol. L. — From edge of tooth socket 

 to edge of tooth socket. 



