Hi Karin
There are huge numbers of possible references out there. You can google
images of sheep skull/cranium/mandible or individual elements: sphenoid, etc.
For general texts with either a single species or multiple species, go to google
books and search:
anatomy
anatomy equine/horse/bovine/cow, etc.
veterinary anatomy...
zoology
anatomy for artists can give some excellent results and many of the texts
are part or fully available online.
Many Vet schools also have anatomy material on their various
websites.
Besides those mentioned already, some standards often used by zooarchs
include:
PALES, L. & LAMBERT, C. 1971. - Atlas Ostéologique pour servir à
I'identification des Mammifères Du Quaternaire: I. Les membres Herbivores.
Centre National de la Recherche Scientifique, Paris. <This looks really nice, but I'm having some lack of agreement
with comparison to actual horses specimens - also I'm not sure this includes the
head...>
SISSON, S., GROSSMAN, J. & GETTY, R. 1975. - Sisson and Grossman's The
anatomy of the domestic animals. . W. B. Saunders Co., Philadelphia.
<excellent text and one edition is available
online...been discussed on zooarch>
Here's some others:
AKERS, R. M. & DENBOW, D. 2008. - Anatomy and Physiology of Domestic
Animals.
ASHDOWN, R. & DONE, S. 1996. - Color atlas of veterinary anatomy: The
horse. Mosby-Wolfe. Elsevier Ltd, London.
BUDRAS, K., SACK, W., RÖCK, S., WÜNSCHE, A. & HENSCHEL, E. 2003. -
Anatomy of the horse: an illustrated text. Schlütersche, Hannover.
BEDDARD, F. 1902. - The CAMBRIDGE NATURAL HISTORY: VOLUME X: MAMMALIA. In
S. F. H. a. A. E. Shipley (ed) Macmillan & Co. Ltd, New York.
CALDERON, W. F. 1936 (1975 reprint). - Animal Painting & Anatomy.
Courier Dover Publications, Mineola (NY).
CHAUVEAU, A., ARLOING, S. & FLEMING, G. 1800. - The comparative anatomy
of the domesticated animals. D. Appleton and Company, New York.
DYCE, K., SACK, W. & WENSING, C. 2009. - Textbook of Veterinary
Anatomy. Saunders/Elsevier, St. Louis.
SCHMITT, E. & WALLACE, S.; 2012; Shape Change and Variation in the
Cranial Morphology of Wild Canids (Canis lupus, Canis latrans, Canis rufus)
Compared to Domestic Dogs (Canis familiaris) Using Geometric Morphometrics;
International Journal of Osteoarchaeology: n/a-n/a;
Schmitt12ShapeChangeVariationCranialMorphWildCanids ReDomDogsGeometricMorph.pdf;
http://dx.doi.org/10.1002/oa.1306.
